CN118813223A - Foam plugging slurry, preparation method of foam plugging slurry, foam plugging slurry system and application - Google Patents

Abstract

The invention relates to the field of petroleum drilling, and discloses foam plugging slurry, a preparation method of the foam plugging slurry, a foam plugging slurry system and application, wherein the foam plugging slurry comprises the following components: cement-based slurries, foaming agents and nitrogen gas filling; wherein the foaming agent is not more than 5 parts by weight relative to 100 parts by weight of the cement-based slurry; the amount of nitrogen added satisfies that the density of the foam plugging slurry is reduced by 3-30% by volume compared to cement-based slurry. The foam plugging slurry disclosed by the invention can flexibly adjust the density according to the inflation proportion, and is suitable for on-site changeable leakage well conditions.

Description

Foam plugging slurry, preparation method of foam plugging slurry, foam plugging slurry system and application

Technical Field

The invention relates to the field of petroleum drilling, and in particular to a foam plugging slurry, a preparation method of the foam plugging slurry, a foam plugging slurry system and applications.

Background Art

Well leakage is often encountered during the oil drilling and cementing process, resulting in a large amount of drilling fluid and other working fluids being lost into the formation. In addition, it takes a long time to plug the leak and withstand the pressure after plugging, which greatly increases the drilling cost.

Usually, the plugging operation is to pump a certain concentration of plugging slurry containing plugging particles of different particle sizes into the leakage layer, and gradually plug the leakage layer through static plugging, pressure-holding plugging or while drilling plugging. When the leakage rate of the local formation exceeds a certain scale (malignant leakage or even loss return), the above plugging effect will be greatly reduced or even completely ineffective.

After conventional plugging slurry enters the formation, it cannot stay at the leaking layer due to its high density under the influence of formation pressure, and leakage occurs at the leaking layer, resulting in plugging failure. In order to solve the problem that cement plugs cannot be retained in formations with low pressure bearing capacity, the density of cement plugs must be reduced as much as possible. Conventional cement plugs are generally limited by the requirements of lightening materials and performance of the slurry entering the well. It is difficult to take into account the various properties of the slurry while maintaining a certain low density of the slurry, resulting in the current density of the cement slurry entering the well not being low enough.

CN103074042A discloses a drilling fluid and a method for preparing the drilling fluid, and discloses a chemical foaming method that relies on chemical agent reaction to generate nitrogen foam. The method is limited by the mixing process and the compatibility with other slurries, and the foaming amount and foam stabilization performance are also limited.

Therefore, it is necessary to design a plugging slurry specifically for the leaking layer with obvious leakage, and cooperate with a certain plugging process to achieve a good plugging effect.

Summary of the invention

The purpose of the present invention is to overcome the problem that conventional plugging slurries in the prior art have unsatisfactory plugging effects, and to provide a foam plugging slurry and a preparation method of the foam plugging slurry, a foam plugging slurry system and an application. The foam plugging slurry has a gas-liquid-solid three-phase flow, a simple and reliable formula, and is easy to use. It meets the low density of the slurry while taking into account various properties of the slurry.

In order to achieve the above-mentioned object, the first aspect of the present invention provides a foam plugging slurry, wherein the foam plugging slurry comprises: a cement-based slurry, a foaming agent and filled nitrogen;

Among them, relative to 100 parts by weight of cement-based slurry, the foaming agent is no more than 5 parts by weight; the filled nitrogen is calculated by volume, and the amount of nitrogen added satisfies that the density of the foam plugging slurry is reduced by 3-30% compared with the cement-based slurry.

A second aspect of the present invention provides a method for preparing a foam plugging slurry, which comprises the following steps:

(1) Prepare cement-based slurry;

(2) adding a foaming agent to the cement-based slurry and stirring evenly to obtain a plugging slurry intermediate;

(3) injecting gas into the plugging slurry intermediate to obtain foam plugging slurry;

Wherein, relative to 100 parts by weight of cement-based slurry, the foaming agent is no more than 5 parts by weight;

Preferably, the nitrogen filled is measured by volume, and the amount of nitrogen added is such that the density of the foam plugging slurry is reduced by 3-30% compared with the cement-based slurry.

The third aspect of the present invention provides a foam plugging slurry, which is prepared by the preparation method described in the second aspect.

The fourth aspect of the present invention provides the aforementioned foam plugging slurry system, comprising the foam plugging slurry described in the first aspect or the third aspect and optional conventional plugging slurry;

Wherein, relative to 100 parts by weight of the foam plugging slurry, the conventional plugging slurry is no more than 100 parts by weight, preferably 10-30 parts by weight.

A fifth aspect of the present invention provides an application of the aforementioned foam plugging slurry or the aforementioned foam plugging slurry system in a shale gas well.

Through the above technical solution, the beneficial technical effects achieved by the present invention are as follows:

(1) The foam plugging slurry of the present invention can flexibly adjust the density according to the inflation ratio, and is suitable for the variable leakage well conditions on site;

(2) The foam plugging slurry of the present invention has unique compressibility, is easier to enter the leaking layer, and has a better plugging effect than conventional plugging slurry;

(3) The foam plugging slurry preparation process of the present invention is simple and low-cost.

DETAILED DESCRIPTION

The endpoints and any values of the ranges disclosed in this article 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 each range, the endpoint values of each range and the individual point values, and the individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

A first aspect of the present invention provides a foam plugging slurry, the foam plugging slurry comprising: a cement-based slurry, a foaming agent and filled nitrogen;

Among them, relative to 100 parts by weight of cement-based slurry, the foaming agent is no more than 5 parts by weight; the filled nitrogen is calculated by volume, and the amount of nitrogen added satisfies that the density of the foam plugging slurry is reduced by 3-30% compared with the cement-based slurry.

According to the present invention, preferably, the nitrogen filled is measured by volume, and the amount of nitrogen added is such that the density of the foam plugging slurry is reduced by 5-20% compared with the cement-based slurry.

In the present invention, the gas volume is controlled by temperature and pressure, and the temperature and pressure are determined by the maximum temperature and leakage pressure of the leaking layer section of each well. Therefore, the required volume of nitrogen is the amount of nitrogen required to reduce the density of the original cement-based slurry by 3-30% (under the maximum temperature and leakage pressure of the leaking layer section), and preferably the density of the original cement-based slurry is reduced by 5-20%. Based on the required amount of nitrogen at this temperature and pressure, the nitrogen charging amount of the ground nitrogen charging equipment (generally referred to as the construction nitrogen charging amount) is inversely deduced through the real nitrogen state equation.

In the present invention, for example, the density of cement slurry is set to 1.88g/ ^cm3 , the maximum temperature of the leaking layer is 90℃, and the well loss pressure is 35MPa. The nitrogen filling volume required to reduce the density of cement slurry by 3%-30% at this temperature and pressure is 0.03-0.53 parts by volume (based on the volume of cement slurry). Based on the required nitrogen filling amount under this temperature and pressure, the ground nitrogen filling volume is reversed according to the real nitrogen state equation to obtain 7-124 parts by volume (based on the volume of cement slurry). That is, relative to the unit volume of cement slurry, the construction nitrogen filling amount required by the ground nitrogen filling equipment is 7-124 parts by volume (based on the volume of cement slurry), so that the foam plugging slurry required by the present invention can be obtained.

According to the present invention, the foaming agent is 2-3 parts by weight, and the foaming agent is an anionic surfactant foaming agent, preferably selected from at least one of sodium dodecylbenzene sulfonate, α-olefin sulfonate, α-sulfo fatty acid methyl ester and sodium N-oleoyl N-methyl taurate.

In some specific embodiments of the present invention, the foaming agent plays a role in foaming and stabilizing foam. When the foaming agent introduces gas by mechanical force, it can effectively reduce the surface tension of the liquid, has a high foaming multiple, good foam stability, can last for a long time without defoaming, has fine foam, and has good compatibility with the medium used.

In the present invention, compared with the use of chemical agents for foaming, it is difficult to control the amount of foaming and the uniformity of foaming. Excessive foaming will destroy the mechanical properties of the base slurry, and insufficient foaming cannot meet the foaming requirements. The present invention uses mechanical physical foaming, which can flexibly respond to different application conditions.

According to the present invention, the cement-based slurry comprises, by weight: 100 parts of cement, 1-10 parts of fluid loss reducer, 0-3 parts of retarder, 0-5 parts of early strength agent, 0-0.2 parts of thickener, and 30-70 parts of water.

According to the present invention, preferably, the cement-based slurry comprises, by weight: 100 parts of cement, 3-8 parts of fluid loss reducer, 0.1-2 parts of retarder, 0.25-1 parts of early strength agent, 0.05-0.1 parts of thickener, and 35-60 parts of water.

In the present invention, preferably, the density of the foam plugging slurry is 1.2-1.7 g/cm ³ .

In the present invention, the cement is pure cement and/or low-density ash mixed with density reducing materials. The mixed density reducing materials are not particularly limited and can be conventional density reducing materials in the art, preferably, at least one selected from floating beads, hollow glass microspheres, microsilica and fly ash.

In the present invention, the fluid loss agent is an emulsion fluid loss agent and/or a water-soluble high molecular polymer fluid loss agent. The use of the above fluid loss agent can control the loss of the liquid phase to the permeability boundary in the cement slurry, thereby maintaining an appropriate water-cement ratio of the cement slurry.

In the present invention, the emulsion fluid loss agent is a latex system fluid loss agent and/or a resin system fluid loss agent, and the water-soluble polymer fluid loss agent is at least one selected from cellulose and its derivatives, acrylamide and its derivatives, and polyvinyl alcohol fluid loss agents. Preferably, the fluid loss agent is acrylamide and/or 2-acrylamido-2-methylpropanesulfonic acid.

In the present invention, the early strength agent is selected from at least one of electrolyte inorganic salt early strength agent, water-soluble organic polymer early strength agent and organic compound and inorganic salt composite early strength agent. In the present invention, the electrolyte inorganic salt early strength agent is selected from at least one of sulfate, sulfate complex salt, nitrate, nitrite and chloride, and the water-soluble organic polymer early strength agent is selected from at least one of triethanolamine, formates, acetates and propionates. The use of the above early strength agent can accelerate the development of early strength of concrete.

In the present invention, preferably, the early strength agent is sodium nitrate and/or triethanolamine.

In the present invention, there is no particular limitation on the type of thickener, and the thickener may be any conventional thickener in the art, such as at least one selected from inorganic thickeners, cellulose thickeners, natural polymer thickeners and their derivatives, synthetic polymer thickeners, and complex organic metal compound thickeners. The above thickeners can improve the viscosity of the cement slurry system.

In the present invention, the inorganic thickener is selected from at least one of organic bentonite, diatomaceous earth, attapulgite and silica gel; preferably, the cellulose thickener is selected from at least one of methyl cellulose, hydroxypropyl methyl cellulose and hydroxyethyl cellulose; preferably, the natural polymer and its derivative thickener is selected from at least one of starch, gelatin, casein, guar gum, xanthan gum and soy protein gum; preferably, the synthetic polymer thickener is selected from at least one of polyacrylamide, polyvinyl alcohol and polyacrylic acid; preferably, the complex organic metal compound thickener is amino alcohol complex titanate.

In the present invention, the retarder is selected from at least one of hydroxycarboxylic acids, aminocarboxylic acids and salts thereof, polyols and derivatives thereof, glucose, sucrose and derivatives thereof, molasses and derivatives thereof, phosphates, metaphosphates, borax and sodium fluorosilicate. The state of the retarder is not particularly limited and may be liquid or solid. The use of the retarder can reduce the cement hydration rate and hydration heat and prolong the setting time.

In the present invention, the water is common well water, river water, river water, rain water, etc. which does not contain obvious minerals and does not affect the basic properties of the cement slurry after mixing.

According to the present invention, there is no particular limitation on the stirring speed, and those skilled in the art can make an adaptive selection according to needs. Preferably, the stirring speed is 5-1000 rpm, preferably 100-500 rpm. At the above stirring speed, uniform mixing of the foam plugging slurry can be achieved.

The present invention develops a special foam plugging slurry, that is, on the basis of conventional density and low-density cement-based slurry, a foaming agent is added and a certain proportion of nitrogen is filled under mechanical action to further reduce the slurry density and form a foam plugging slurry with uniform foam, so as to achieve the goal of basically no leakage when plugging cement plugs (plugging cement slurry) in strata with low pressure bearing capacity, thereby ensuring the success rate of plugging.

A second aspect of the present invention provides a method for preparing a foam plugging slurry, which comprises the following steps:

(1) Prepare cement-based slurry;

(2) adding a foaming agent to the cement-based slurry and stirring evenly to obtain a plugging slurry intermediate;

(3) filling nitrogen into the plugging slurry intermediate to obtain foam plugging slurry;

Wherein, relative to 100 parts by weight of cement-based slurry, the foaming agent is no more than 5 parts by weight;

Preferably, the nitrogen gas charged is calculated on a volume basis to ensure that the density of the foam plugging slurry decreases by 3-30% compared to when no nitrogen gas is added.

In some specific embodiments, the gas density is approximately calculated according to the real gas state equation or obtained by looking up the table based on the published experimental data table of gas at different temperatures and pressures. For example, at temperature T1 and pressure P1, the gas density is D1, and the cement-based slurry density is C1. Then, each unit volume of cement-based slurry is filled with n unit volumes of gas at this temperature and pressure and mixed evenly to form a uniform gas-liquid-solid three-phase flow foam plugging slurry. The density is approximately F1(T1, P1) = (n×D1+C1)/(n+1). As n increases, the amount of gas filled increases, and the density of the foam plugging slurry is lower.

In some specific embodiments of the present invention, the nitrogen filling process in step (3) comprises:

(3-1) Simulation calculation: Under the highest temperature and leakage pressure of the leaking layer, a certain volume of nitrogen is charged into the plugging slurry intermediate (which can be a sample liquid that meets the aforementioned composition of the present invention but has a smaller amount) to obtain a foam plugging slurry. The density of the foam plugging slurry is reduced by 3-30%, preferably 5-20%, compared with the density of the cement-based slurry. That is, the density of the foam plugging slurry is 70-97%, preferably 80-95% of the density of the cement-based slurry. The density of the formed foam plugging slurry approximately satisfies the following relationship: F(T,P)=(n×D+C)/(n+1). For example, at the highest temperature T1 and leakage pressure P1 of the leaking layer, the nitrogen density is D1, and the cement-based slurry density is C1. Then, the cement-based slurry is filled with n unit volumes of nitrogen at this temperature and pressure and mixed evenly to obtain a foam plugging slurry. The density of the foam plugging slurry is 70-97% of the density of the base liquid, preferably 80-95%. Based on this, the required amount of nitrogen at the highest temperature and leakage pressure of the leaking layer is obtained, and then the required nitrogen filling amount on the ground (temperature and ground pressure under the ground environment) is reversed according to the real nitrogen state equation to obtain the construction nitrogen filling amount;

(3-2) Using a special nitrogen filling device, nitrogen is filled into the plugging slurry intermediate according to the construction nitrogen filling amount obtained above (the amount used meets the construction nitrogen filling amount required for the plugging slurry intermediate), to obtain foam plugging slurry.

The density of nitrogen is different at different temperatures and pressures. It can be approximately calculated based on the real gas state equation or obtained by looking up the published experimental data table of nitrogen at different temperatures and pressures.

According to the present invention, preferably, the foaming agent is 2-3 parts by weight relative to 100 parts by weight of the cement-based slurry.

According to the present invention, preferably, the nitrogen gas charged is calculated on a volume basis to satisfy that the density of the foam plugging slurry is reduced by 5-20% compared to when no nitrogen gas is added.

According to the present invention, the cement-based slurry in step (1) comprises, by weight: 100 parts of cement, 1-10 parts of fluid loss agent, 0-3 parts of retarder, 0-5 parts of early strength agent, 0-0.2 parts of thickener, and 30-70 parts of water. Further, the cement-based slurry comprises, by weight: 100 parts of cement, 3-8 parts of fluid loss agent, 0.1-2 parts of retarder, 0.25-1 parts of early strength agent, 0.05-0.1 parts of thickener, and 35-60 parts of water.

In some embodiments, after the cement-based slurry described in step (1) is prepared, various properties of the cement-based slurry are evaluated at the highest temperature and leakage pressure at the depth of the leaking layer, including cold and hot slurry rheology (cold and hot slurry six-speed rheometer tail turn value ≥ 10), API water loss (30min water loss <100mL), thickening curve (the curve is normal, meeting the safety time and construction conditions for downhole pumping to the leaking layer) and compressive strength (compressive strength >3MPa after curing for 48h at the lowest temperature and leakage pressure of the leaking layer). If the cement-based slurry meets the above properties, it meets the requirements for further preparation of foam plugging slurry.

In some embodiments, according to the bearing capacity of the formation of the leakage layer, a certain volume and density of cement slurry that can cover the thickness of the leakage layer is prepared (the density of the foam plugging slurry at the leakage layer in the wellbore is required to be low enough, and the slurry pressure at this place is equivalent to the leakage pressure of the formation at this place, so that this section of cement slurry can stay and wait for solidification and strength, otherwise the cement slurry will leak at the leakage layer, and will be completely lost or partially lost, causing plugging failure), and then combined with a certain cement slurry injection process, it is pumped to the leakage formation position and waited for solidification for 24-72 hours. After the cement slurry is completely thickened and strengthened, a cement plug with a certain strength bonded to the formation is formed. At this time, the cement plug completely blocks and seals the leakage channels such as holes, cracks and holes in the original leakage formation. Then, the cement plug in this section of the wellbore is swept away by drilling, and the wall of the leakage layer in this section is strengthened by cement solidification, which can greatly alleviate or eliminate the leakage of the leakage layer, so that normal drilling can continue.

The third aspect of the present invention provides a foam plugging slurry, which is prepared by the preparation method described in the second aspect.

The fourth aspect of the present invention provides the aforementioned foam plugging slurry system, comprising the foam plugging slurry described in the first aspect or the third aspect and optional conventional plugging slurry;

Wherein, relative to 100 parts by weight of the foam plugging slurry, the conventional plugging slurry is no more than 100 parts by weight, preferably 10-30 parts by weight.

In the present invention, the foam plugging slurry is mixed with conventional plugging slurry to further improve the plugging performance of the foam plugging slurry. There is basically no leakage when plugging cement plugs (plugging cement slurry) in formations with low pressure bearing capacity, thereby ensuring the success rate of plugging.

A fifth aspect of the present invention provides an application of the aforementioned foam plugging slurry or the aforementioned foam plugging slurry system in a shale gas well.

The present invention will be described in detail below through examples and comparative examples. In the following examples and comparative examples, if no specific conditions are specified, the experiments were carried out under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used, if the manufacturer is not specified, are all conventional or customized products that can be obtained through commercial channels.

Example 1

(1) The maximum temperature of the leaking layer section is set at 90°C and the overburden pressure is 35 MPa. The cement-based slurry is prepared according to the weight ratio of 100 parts of cement, 3 parts of fluid loss reducer, 2 parts of retarder, 0.25 parts of early strength agent, 0.05 parts of thickener, and 50 parts of water. The cement density is 1.88 g/cm ³ . The specific formula is shown in Table 1;

(2) adding 3 parts by weight of a foaming agent to the cement-based slurry and stirring at a speed of 100 rpm for 3 minutes to obtain a plugging slurry intermediate;

(3) Assume that the ground nitrogen filling equipment fills the plugging slurry intermediate with nitrogen 50 times the volume of the base slurry to obtain foam plugging slurry (1 atmosphere, 20°C). The foam plugging slurry of this density is equivalent to the formation loss pressure of this leaking layer after superimposing all the upper pressures on this leaking layer.

Example 2

The foam plugging slurry was prepared according to the steps of Example 1. The specific formula is shown in Table 1.

Example 3

The foam plugging slurry was prepared according to the steps of Example 1. The specific formula is shown in Table 1.

Example 4

The foam plugging slurry was prepared according to the steps of Example 1. The specific formula is shown in Table 1.

Example 5

The foam plugging slurry was prepared according to the steps of Example 1. The specific formula is shown in Table 1.

Table 1

Comparative Example 1

The foam plugging slurry was prepared according to the set conditions and steps of Example 1, except that no gas was added. The specific formula is shown in Table 2.

Comparative Example 2

The foam plugging slurry was prepared according to the set conditions and steps of Example 1. The specific formula is shown in Table 2.

Comparative Example 3

The foam plugging slurry was prepared according to the set conditions and steps of Example 1, except that no foaming agent was added. The specific formula is shown in Table 2.

Comparative Example 4

The foam plugging slurry was prepared according to the set conditions and steps of Example 1, except that no retarder was added. The specific formula is shown in Table 2.

Comparative Example 5

The foam plugging slurry was prepared according to the steps of Example 1, except that no fluid loss agent was added. The specific formula is shown in Table 2.

Table 2

Test Example 1

The various performance indicators of the cement-based slurries of the embodiments and comparative examples were tested, and the results are shown in Table 3. The rheology of the cold and hot slurries was read using a six-speed rotary viscometer;

API water loss is measured using a high temperature and high pressure water loss instrument in accordance with API standards;

The thickening curve is obtained using a pressurized thickening instrument according to the conventional practice in the industry;

The compressive strength was tested on cement specimens cured for 48 hours using a pressure testing machine.

Table 3

Test Example 2

The performance parameter measurement results of the foam plugging slurry of the embodiment and the comparative example are shown in Table 4.

Table 4

It can be seen from Table 4 that the foam plugging slurry of Example 1 and Example 2, the cement-based slurry performance meets the safety time and construction conditions of downhole pumping to the leaking layer, the foam plugging slurry at the leaking layer is a uniform bubbling flow without leakage, and the bubbles are stably distributed without free, the slurry stability is good, and the plugging effect is better than that of the foam plugging slurry of the comparative example.

Test Example 3

The plugging performance of the foam plugging slurry of Example 1 and Example 2 was tested, and the results are shown in Table 5.

Table 5

As can be seen from Table 5, the foam plugging slurry of Example 1 and Example 2 of the present invention was used. At the Chongqing Nanchuan shale gas field, the formula and preparation method of the foam plugging slurry of the present invention were applied. The plugging effect of the conventional plugging scheme in the early stage was not ideal. Finally, the foam plugging slurry was used to plug the leaking layer, and the plugging effect was significant. The plugging was successful in one time, saving a lot of plugging costs.

The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims (10)

1. A foam plugging slurry, wherein the foam plugging slurry comprises: cement-based slurries, foaming agents and nitrogen gas filling;

Wherein the foaming agent is not more than 5 parts by weight relative to 100 parts by weight of the cement-based slurry; the amount of nitrogen added satisfies that the density of the foam plugging slurry is reduced by 3-30% by volume compared to cement-based slurry.

2. The foam plugging slurry of claim 1 wherein the foaming agent is 2-3 parts by weight;

Preferably, the amount of nitrogen added is such that the density of the foam plugging slurry is reduced by 5-20% by volume compared to the cement-based slurry.

3. The foam plugging slurry of claim 1 or 2, wherein the cement-based slurry comprises, in parts by weight: 100 parts of cement, 1-10 parts of a fluid loss agent, 0-3 parts of a retarder, 0-5 parts of an early strength agent, 0-0.2 part of a thickener and 30-70 parts of water;

preferably, the cement-based slurry comprises, in parts by weight: 100 parts of cement, 3-8 parts of filtrate reducer, 0.1-2 parts of retarder, 0.25-1 part of early strength agent, 0.05-0.1 part of thickener and 35-60 parts of water.

4. The preparation method of the foam leak-stopping slurry is characterized by comprising the following steps of:

(1) Preparing cement-based slurry;

(2) Adding a foaming agent into the cement-based slurry, and uniformly stirring to obtain a leakage blocking slurry intermediate;

(3) Filling nitrogen into the middle of the plugging slurry to obtain foam plugging slurry;

wherein the foaming agent is not more than 5 parts by weight relative to 100 parts by weight of the cement-based slurry;

Preferably, the amount of nitrogen added is such that the density of the foam plugging slurry is reduced by 3-30% by volume compared to the cement-based slurry.

5. The preparation method according to claim 4, wherein the cement-based slurry in step (1) comprises, in parts by weight: 100 parts of cement, 1-10 parts of a fluid loss agent, 0-3 parts of a retarder, 0-5 parts of an early strength agent, 0-0.2 part of a thickener and 30-70 parts of water;

preferably, the cement-based slurry comprises, in parts by weight: 100 parts of cement, 3-8 parts of filtrate reducer, 0.1-2 parts of retarder, 0.25-1 part of early strength agent, 0.05-0.1 part of thickener and 35-60 parts of water.

6. The production method according to claim 4 or 5, wherein the foaming agent is2 to 3 parts by weight relative to 100 parts by weight of the cement-based slurry;

preferably, the amount of nitrogen added is such that the density of the foamed plugging slurry is reduced by 5-20% by volume compared to the cement-based slurry;

Preferably, the foaming agent in the step (2) is a surfactant foaming agent, preferably at least one selected from sodium dodecyl benzene sulfonate, alpha-olefin sulfonate, alpha-sulfo fatty acid methyl ester and sodium N-oleoyl-N-methyl taurate;

preferably, the stirring speed is 50-1000rpm, preferably 100-500rpm.

7. The preparation method according to any one of claims 4 to 6, wherein the fluid loss additive is an emulsion fluid loss additive and/or a water-soluble high polymer fluid loss additive;

preferably, the early strength agent is at least one selected from electrolyte inorganic salt early strength agents, water-soluble organic polymer early strength agents and organic compound and inorganic salt composite early strength agents.

8. A foam plugging slurry prepared by the preparation method of any one of claims 4-7.

9. A foamed plugging slurry system, characterized in that the system comprises the foamed plugging slurry of any one of claims 1-3, 8 and optionally a conventional plugging slurry;

wherein the conventional plugging slurry is not more than 100 parts by weight, preferably 10 to 30 parts by weight, relative to 100 parts by weight of the foam plugging slurry.

10. Use of the foamed plugging slurry of any one of claims 1-3, 8 or the foamed plugging slurry system of claim 9 in a shale gas well.