An annulus pressure management plugging agent, a preparation method and application thereof

Abstract

The application provides a plugging agent for treating annular pressure, and a preparation method and application thereof. The plugging agent comprises urease activity liquid and superfine cement plugging paste. The urease activity liquid comprises urease-producing bacteria liquid and / or urease liquid, and is used for inducing the production of carbonate. The superfine cement plugging paste comprises superfine cement base material and calcium-containing early strength agent, and the average particle size D 50 of the superfine cement base material is ≤30 μm. The volume ratio of the urease activity liquid to the superfine cement plugging paste is (2-4):1. The plastic viscosity of the plugging agent is 5-30 mpa·s. The plugging agent provided by the application can effectively plug small-size micro cracks, improve the treatment effect of annular pressure, improve environmental protection, reduce production and construction operation cost, and is conducive to large-scale popularization and application.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas extraction technology, and relates to a plugging agent for controlling annular pressure, and more particularly to a plugging agent for controlling annular pressure, its preparation method and application. Background Technology

[0002] With the increase in oil and gas production, the annular pressure phenomenon in oil and gas wells is becoming increasingly common, posing a serious threat to safe production. During the extraction of oil and gas wells, the annular space between the casing layers within the wellbore needs to be filled with cement to form several annular barriers composed of multiple layers of casing and cement. These annular barriers not only seal the annulus but also prevent the infiltration of underground oil, gas, water, and other fluids, thereby ensuring safe construction and extraction in subsequent stages.

[0003] The main causes of annular pressure include: (1) damage to the integrity of the cement sheath; (2) failure of the bonding between the cement sheath and the casing or failure of the bonding between the cement sheath and the formation. The presence of annular pressure in oil and gas wells will have many impacts on the production of oil and gas wells, such as: reducing the recovery rate of oil and gas wells, affecting subsequent operations, increasing the cost of wellhead annular pressure monitoring and depressurization year by year, and even causing blowout accidents in severe cases.

[0004] Currently, the main methods for managing annular pressure are well workovers and the injection of sealing materials such as cement and resin into the annulus to re-seal fluid channels, including micro-cracks in the cement sheath. However, because the cracks in the cement sheath are very small, materials containing solid phases cannot fully penetrate and fill them. Injecting cement into the annulus is difficult, dangerous, and has a low success rate. Therefore, developing a high-performance novel sealing agent system has become crucial for effectively solving the annular pressure problem.

[0005] CN113930200A discloses a sealant for treating annular pressure, its preparation method, and its application. The sealant comprises a composite resin, a curing agent, a toughening agent, and a viscosity reducer. This sealant is extruded from the surface annulus into the annulus of an oil and gas well and cured to seal micro-cracks in the cement sheath, effectively sealing the annulus and solving the problem of casing punctures with pressure. However, the sealant has a high viscosity (1000–1500 MPa·s), making it unable to effectively seal small-sized micro-cracks. Furthermore, the sealant suffers from poor environmental performance and high production and construction costs.

[0006] Furthermore, microbial-induced calcium carbonate precipitation (MICP) technology, as an emerging method for geological engineering reinforcement, is gradually gaining prominence and becoming a focus of research in various fields due to its environmentally friendly, low-energy-consumption, pollution-free, and highly efficient characteristics. MICP produces crystalline and non-crystalline inorganic compounds through metabolism, thereby playing a filling and binding role in the soil and further improving the properties of soil and concrete.

[0007] CN109594552A discloses a method for combined microbial solidification and fiber reinforcement modification of sand. Addressing the increased brittleness of microbially solidified sand, basalt fiber, carbon fiber, and steel fiber are incorporated into the MIP (Microbial-Induced Polymerization) technology to improve the brittleness of the solidified sand and enhance its residual strength and toughness. CN111749227A discloses a method for inducing carbonate precipitation using microorganisms combined with rubber materials. Rubber particles are incorporated into the MIP technology to improve the liquefaction resistance of solidified sand. However, since MIP technology has not yet been applied in the cementing field, many problems remain in both laboratory and field tests, requiring further in-depth research. The most important aspect is its application in annular pressure control.

[0008] Therefore, it is evident that providing a plugging agent for treating annular pressure based on microbial-induced calcium carbonate precipitation technology, and its preparation method, particularly for effectively sealing small-sized microcracks, improving the treatment effect of annular pressure, while enhancing environmental friendliness and reducing production and construction costs, has become an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0009] To address the shortcomings of existing technologies, the present invention aims to provide a sealing agent for treating annular pressure, its preparation method, and its application. The sealing agent effectively seals small-sized microcracks, improves the treatment effect of annular pressure, enhances environmental friendliness, reduces production and construction costs, and facilitates large-scale promotion and application.

[0010] To achieve this objective, the present invention adopts the following technical solution:

[0011] In a first aspect, the present invention provides a sealing agent for treating annular pressure, the sealing agent comprising urease active liquid and ultrafine cement sealing grout.

[0012] The urease active solution includes urease-producing bacterial solution and / or urease solution, used to induce the production of carbonate ions.

[0013] The ultrafine cement sealing grout comprises an ultrafine cement base material and a calcium-containing early-strength agent, wherein the average particle size D of the ultrafine cement base material is... 50 ≤30μm, for example, can be 1μm, 5μm, 10μm, 15μm, 20μm, 25μm or 30μm, but is not limited to the listed values, other unlisted values ​​within this range also apply.

[0014] The volume ratio of the urease active liquid to the ultrafine cement sealing grout is (2-4):1, for example, it can be 2:1, 2.2:1, 2.4:1, 2.6:1, 2.8:1, 3:1, 3.2:1, 3.4:1, 3.6:1, 3.8:1 or 4:1, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0015] The plastic viscosity of the plugging agent is 5-30 mPa·s, for example, it can be 5 mPa·s, 10 mPa·s, 15 mPa·s, 20 mPa·s, 25 mPa·s or 30 mPa·s, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0016] The sealing agent provided by this invention induces the generation of carbonate ions through urease active liquid, and provides calcium ions with the help of calcium-containing early strength agent in ultrafine cement sealing slurry. The carbonate ions combine with calcium ions to form calcium carbonate deposits. Subsequently, calcium carbonate crystals continuously accumulate, gradually compressing the internal pore space of the cement ring body during the treatment of annular pressure. Macroscopically, this manifests as filling of cement ring cracks, reducing permeability, and increasing interfacial bonding strength.

[0017] Furthermore, by limiting the volume ratio of urease active liquid to ultrafine cement sealing slurry within a reasonable range, this invention maintains the solid content in the sealing agent at a low level and has low plastic viscosity. This facilitates the full injection of the sealing agent into the microcracks of the cement annulus, reduces the annular pumping pressure and construction costs, and avoids the situation where the sealing agent cannot enter the microcracks due to filtration loss caused by the presence of solid particles. Thus, it effectively seals small-sized microcracks and improves the treatment effect of annular pressure.

[0018] The sealing agent provided by this invention can be cured at room temperature, thus enabling the treatment of annular pressure caused by cement ring integrity failure in shallow formations. At the same time, the sealing agent is environmentally friendly, improving its environmental protection and facilitating large-scale promotion and application.

[0019] Preferably, the urease-producing bacterial solution comprises urease-producing bacteria, an inducer, and deionized water.

[0020] Preferably, the urease solution comprises urease, an inducer, and deionized water.

[0021] Preferably, the urease-producing bacteria include Bacillus pasteurellii, and the bacterial cell density OD 600 The range is 0.5-1.0, for example, it can be 0.5, 0.6, 0.7, 0.8, 0.9 or 1.0, but it is not limited to the listed values. Other unlisted values ​​within this range also apply.

[0022] Preferably, the concentration of the urease is 3.0-10.0 g / L, for example, it can be 3.0 g / L, 4.0 g / L, 5.0 g / L, 6.0 g / L, 7.0 g / L, 8.0 g / L, 9.0 g / L or 10.0 g / L, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0023] Preferably, the inducing agent comprises urea, and the concentration of the urea is 0.05-0.15 mol / L, for example, it can be 0.05 mol / L, 0.06 mol / L, 0.07 mol / L, 0.08 mol / L, 0.09 mol / L, 0.10 mol / L, 0.11 mol / L, 0.12 mol / L, 0.13 mol / L, 0.14 mol / L or 0.15 mol / L, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0024] Preferably, the ultrafine cement sealing grout comprises the following components by weight:

[0025]

[0026] The highly active material comprises 5-20 parts by weight, for example, 5, 6, 8, 10, 12, 14, 16, 18, or 20 parts; the calcium-containing early-strength agent comprises 1-6 parts by weight, for example, 1, 2, 3, 4, 5, or 6 parts; the organic early-strength agent comprises 0.05-1 part by weight, for example, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or 1 part; and the dispersant comprises 0.5-2 parts by weight, for example, 0.5 parts. The weight percentages of the defoamer are 0.1-1 parts, for example, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or 1 part; the weight percentages of the deionized water are 30-50 parts, for example, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, or 50 parts, but are not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0027] Preferably, the specific surface area of ​​the ultrafine cementitious substrate material is ≥1000 m². 2 / kg, for example, could be 1000m 2 / kg, 1500m 2 / kg, 2000m 2 / kg, 2500m 2 / kg, 3000m 2 / kg, 3500m 2 / kg, 4000m 2 / kg, 4500m 2 / kg or 5000m 2 / kg, but not limited to the listed values; other unlisted values ​​within this range also apply.

[0028] In this invention, the highly active material refers to an oil well cement admixture with high hydration activity, which, when activated by an early-strength agent, can shorten the initial setting time of cement slurry and improve the early strength of cement stone.

[0029] Preferably, the highly active material includes any one or a combination of at least two of sulfoaluminate, microsilica, or metakaolin fly ash. Typical but not limited combinations include a combination of sulfoaluminate and microsilica, a combination of microsilica and metakaolin fly ash, a combination of sulfoaluminate and metakaolin fly ash, or a combination of sulfoaluminate, microsilica, and metakaolin fly ash.

[0030] In this invention, the aforementioned highly active material can significantly accelerate the deposition of calcium ions, increase the total mass of deposited calcium carbonate, and ensure that the microbial-induced calcium carbonate deposition process can continue even when the amount of reaction solution is increased.

[0031] Preferably, the calcium-containing early strength agent includes any one or a combination of at least two of calcium chloride, calcium sulfate, or calcium nitrate. Typical but non-limiting combinations include a combination of calcium chloride and calcium sulfate, a combination of calcium sulfate and calcium nitrate, a combination of calcium chloride and calcium nitrate, or a combination of calcium chloride, calcium sulfate, and calcium nitrate.

[0032] On the one hand, the calcium-containing early-strength agent can shorten the setting time of ultrafine cement sealing grout and improve the compressive strength of cement stone; on the other hand, the calcium-containing early-strength agent provides a calcium source for urease active liquid, maintaining the continuous process of microbial-induced calcium carbonate deposition.

[0033] Preferably, the organic early strength agent comprises calcium oxalate and / or triethanolamine.

[0034] On the one hand, the organic early strength agent can improve the compressive strength of cement stone; on the other hand, C, H, O, and N are its main constituent elements, which can provide additional carbon and nitrogen sources and other nutrients required for the growth of urease-producing bacteria, thus better promoting bacterial growth, increasing urease activity and calcium carbonate production, and enhancing the reinforcement and seepage prevention effect of cement rings.

[0035] In this invention, the dispersant and defoamer are both commonly used blocking agent components in the art. As long as they can achieve the corresponding dispersion and defoaming functions, they are acceptable. Therefore, no specific type or model of dispersant and defoamer is specifically limited here.

[0036] In a second aspect, the present invention provides a method for preparing the blocking agent as described in the first aspect, the method comprising the following steps:

[0037] (1) Preparation of urease active solution;

[0038] (2) Prepare ultrafine cement sealing grout;

[0039] (3) Mix urease active liquid and ultrafine cement sealing grout to obtain sealing agent.

[0040] Steps (1) and (2) are not in any particular order.

[0041] Preferably, the urease active solution in step (1) includes urease-producing bacterial solution and / or urease solution.

[0042] Preferably, the method for preparing the urease-producing bacterial solution includes the following steps:

[0043] (a) Yeast extract, sodium chloride and inducer were added to deionized water and mixed evenly to prepare fermentation medium;

[0044] (b) Sterilize the fermentation medium;

[0045] (c) Inoculate the fermentation medium with urease-producing bacteria and culture it under stirring conditions to obtain a urease-producing bacterial solution.

[0046] Preferably, the concentration of yeast extract in the fermentation medium in step (a) is 15-25 g / L, for example, it can be 15 g / L, 16 g / L, 17 g / L, 18 g / L, 19 g / L, 20 g / L, 21 g / L, 22 g / L, 23 g / L, 24 g / L or 25 g / L, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0047] Preferably, the concentration of sodium chloride in the fermentation medium in step (a) is 4-6 g / L, for example, it can be 4 g / L, 4.2 g / L, 4.4 g / L, 4.6 g / L, 4.8 g / L, 5 g / L, 5.2 g / L, 5.4 g / L, 5.6 g / L, 5.8 g / L or 6 g / L, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0048] Preferably, the concentration of the inducer in the fermentation medium in step (a) is 0.05-0.15 mol / L, for example, it can be 0.05 mol / L, 0.06 mol / L, 0.07 mol / L, 0.08 mol / L, 0.09 mol / L, 0.10 mol / L, 0.11 mol / L, 0.12 mol / L, 0.13 mol / L, 0.14 mol / L or 0.15 mol / L, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0049] Preferably, the inducing agent comprises urea.

[0050] Preferably, the pH value of the fermentation medium in step (a) is 7-9, for example, it can be 7, 7.2, 7.4, 7.6, 7.8, 8, 8.2, 8.4, 8.6, 8.8 or 9, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0051] Preferably, the sterilization temperature in step (b) is 115-125°C, for example, it can be 115°C, 116°C, 117°C, 118°C, 119°C, 120°C, 121°C, 122°C, 123°C, 124°C or 125°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0052] Preferably, the sterilization time in step (b) is 20-40 min, for example, it can be 20 min, 22 min, 24 min, 26 min, 28 min, 30 min, 32 min, 34 min, 36 min, 38 min or 40 min, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0053] Preferably, the stirring speed in step (c) is 100-140 rpm, for example, it can be 100 rpm, 105 rpm, 110 rpm, 115 rpm, 120 rpm, 125 rpm, 130 rpm, 135 rpm or 140 rpm, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0054] Preferably, the culture temperature in step (c) is 25-35°C, for example, it can be 25°C, 26°C, 27°C, 28°C, 29°C, 30°C, 31°C, 32°C, 33°C, 34°C or 35°C, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0055] Preferably, the incubation time in step (c) is 12-24h, for example, it can be 12h, 14h, 16h, 18h, 20h, 22h or 24h, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0056] As a preferred embodiment of the second aspect of the present invention, the preparation method includes the following steps:

[0057] (1) Preparation of urease active solution; the urease active solution includes urease-producing bacterial solution and / or urease solution, and the preparation method of the urease-producing bacterial solution is as follows:

[0058] (a) Yeast extract, sodium chloride and urea are added to deionized water and mixed evenly to prepare a fermentation medium with a pH of 7-9; the concentration of yeast extract in the fermentation medium is 15-25 g / L, the concentration of sodium chloride is 4-6 g / L and the concentration of urea is 0.05-0.15 mol / L.

[0059] (b) Sterilize the fermentation medium at 115-125℃ for 20-40 minutes;

[0060] (c) Inoculate the fermentation medium with urease-producing bacteria, and culture it under stirring conditions of 100-140 rpm, at a temperature of 25-35℃, for 12-24 h to obtain urease-producing bacterial solution;

[0061] (2) Prepare ultrafine cement sealing grout;

[0062] (3) Mix urease active liquid and ultrafine cement sealing grout in a volume ratio of (2-4):1 to obtain the sealing agent.

[0063] Steps (1) and (2) are not in any particular order.

[0064] Thirdly, the present invention provides an application of the plugging agent as described in the first aspect, the plugging agent being used to manage annular pressure.

[0065] Preferably, the treatment of annular pressure includes any one of the following two methods:

[0066] (A) The plugging agent is injected directly into the annulus through a phased circulation process from the wellhead;

[0067] (B) First, inject urease active solution directly, and then inject ultrafine cement sealing grout in batches.

[0068] In method (A), a sealing agent is obtained by combining urease active liquid with ultrafine cement sealing grout. The ultrafine cement sealing grout serves as a matrix material for filling cracks and leaks, and is used to fill the pores between cement hydration products. The urease active liquid has a low plastic viscosity, which allows it to enter and seal smaller diameter channels and gaps.

[0069] In method (B), direct injection of urease active solution can induce calcium carbonate precipitation through microorganisms, forming a stable three-dimensional network structure in microcracks, small-diameter pores and between sand particles, which plays a role in the initial consolidation of the cement ring body and interface.

[0070] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0071] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0072] (1) The sealing agent provided by the present invention induces carbonate ions through urease active liquid and provides calcium ions with the help of calcium-containing early strength agent in ultrafine cement sealing slurry. The carbonate ions combine with calcium ions to form calcium carbonate deposits. Subsequently, calcium carbonate crystals continuously accumulate, gradually compressing the internal pore space of the cement ring body during the treatment of annular pressure. Macroscopically, this manifests as filling of cement ring cracks, reducing permeability, and increasing interfacial bonding strength.

[0073] (2) By limiting the volume ratio of urease active liquid and ultrafine cement sealing slurry within a reasonable range, the present invention maintains the solid content in the sealing agent at a low level and has a low plastic viscosity, which is conducive to the full injection of the sealing agent into the microcracks of the cement ring, reducing the annular pumping pressure and construction operation cost, and avoiding the situation where the sealing agent cannot enter the microcracks due to the filtration phenomenon caused by the presence of solid particles. Thus, it forms an effective seal for small-sized microcracks and improves the treatment effect of annular pressure.

[0074] (3) The sealing agent provided by the present invention can be cured at room temperature, and can then be used to treat annular pressure caused by cement ring integrity failure in shallow formations. At the same time, the sealing agent is environmentally friendly and its environmental protection is significantly better than that of traditional resin-based sealing agents, which is conducive to large-scale promotion and application. Detailed Implementation

[0075] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0076] Example 1

[0077] This embodiment provides a sealing agent for treating annular pressure. The sealing agent comprises urease-producing bacterial solution and ultrafine cement sealing slurry, and the volume ratio of the urease-producing bacterial solution to the ultrafine cement sealing slurry is 3:1. The plastic viscosity of the sealing agent is 20 MPa·s.

[0078] Specifically, the urease-producing bacterial solution includes urease-producing bacteria, urea, and deionized water, and the urease-producing bacteria include Bacillus pasteurellii, with a bacterial density OD... 600 The concentration of urea is 0.8; the concentration of urea is 0.10 mol / L.

[0079] The ultrafine cement sealing grout comprises the following components by weight:

[0080]

[0081] In this embodiment, the average particle size D of the ultrafine cementitious substrate material 50 It has a diameter of 25 μm and a specific surface area of ​​1500 m². 2 / kg.

[0082] This embodiment also provides a method for preparing the above-mentioned blocking agent, the preparation method comprising the following steps:

[0083] (1) Preparation of urease-producing bacterial culture, the specific process is as follows:

[0084] (a) Yeast extract, sodium chloride and urea were added to deionized water and mixed evenly to prepare a fermentation medium with a pH of 8; the concentration of yeast extract in the fermentation medium was 20 g / L, the concentration of sodium chloride was 5 g / L and the concentration of urea was 0.10 mol / L.

[0085] (b) Sterilize the fermentation medium at 120°C for 30 min;

[0086] (c) Inoculate the fermentation medium with urease-producing bacteria, and culture it under stirring at 120 rpm and at a temperature of 30°C for 18 h to obtain urease-producing bacterial solution.

[0087] (2) Prepare ultrafine cement sealing grout according to the set weight proportions;

[0088] (3) Mix urease-producing bacterial solution and ultrafine cement sealing grout in a volume ratio of 3:1 to obtain the sealing agent.

[0089] Example 2

[0090] This embodiment provides a sealing agent for treating annular pressure. The sealing agent includes urease-producing bacterial solution and ultrafine cement sealing slurry, and the volume ratio of the urease-producing bacterial solution to the ultrafine cement sealing slurry is 2:1. The plastic viscosity of the sealing agent is 30 MPa·s.

[0091] Specifically, the urease-producing bacterial solution includes urease-producing bacteria, urea, and deionized water, and the urease-producing bacteria include Bacillus pasteurellii, with a bacterial density OD... 600 The value is 1.0; the concentration of the urea is 0.15 mol / L.

[0092] The ultrafine cement sealing grout comprises the following components by weight:

[0093]

[0094] In this embodiment, the average particle size D of the ultrafine cementitious substrate material 50 It has a diameter of 30 μm and a specific surface area of ​​1000 m². 2 / kg.

[0095] This embodiment also provides a method for preparing the above-mentioned blocking agent, the preparation method comprising the following steps:

[0096] (1) Preparation of urease-producing bacterial culture, the specific process is as follows:

[0097] (a) Yeast extract, sodium chloride and urea were added to deionized water and mixed evenly to prepare a fermentation medium with a pH of 7; the concentration of yeast extract in the fermentation medium was 25 g / L, the concentration of sodium chloride was 6 g / L and the concentration of urea was 0.15 mol / L.

[0098] (b) Sterilize the fermentation medium at 115°C for 40 min;

[0099] (c) Inoculate the fermentation medium with urease-producing bacteria, and culture it under stirring at 100 rpm at a temperature of 25°C for 24 h to obtain urease-producing bacterial solution.

[0100] (2) Prepare ultrafine cement sealing grout according to the set weight proportions;

[0101] (3) Mix urease-producing bacterial solution and ultrafine cement sealing grout in a volume ratio of 2:1 to obtain the sealing agent.

[0102] Example 3

[0103] This embodiment provides a sealing agent for treating annular pressure. The sealing agent comprises urease-producing bacterial solution and ultrafine cement sealing slurry, and the volume ratio of the urease-producing bacterial solution to the ultrafine cement sealing slurry is 4:1. The plastic viscosity of the sealing agent is 5 MPa·s.

[0104] Specifically, the urease-producing bacterial solution includes urease-producing bacteria, urea, and deionized water, and the urease-producing bacteria include Bacillus pasteurellii, with a bacterial density OD... 600 The concentration of urea is 0.05 mol / L.

[0105] The ultrafine cement sealing grout comprises the following components by weight:

[0106]

[0107]

[0108] In this embodiment, the average particle size D of the ultrafine cementitious substrate material 50 It has a diameter of 20 μm and a specific surface area of ​​2000 m². 2 / kg.

[0109] This embodiment also provides a method for preparing the above-mentioned blocking agent, the preparation method comprising the following steps:

[0110] (1) Preparation of urease-producing bacterial culture, the specific process is as follows:

[0111] (a) Yeast extract, sodium chloride and urea were added to deionized water and mixed evenly to prepare a fermentation medium with a pH of 9; the concentration of yeast extract in the fermentation medium was 15 g / L, the concentration of sodium chloride was 4 g / L and the concentration of urea was 0.05 mol / L.

[0112] (b) Sterilize the fermentation medium at 125°C for 20 min;

[0113] (c) Inoculate the fermentation medium with urease-producing bacteria, and culture it under stirring at 140 rpm and at a temperature of 35°C for 12 h to obtain urease-producing bacterial solution.

[0114] (2) Prepare ultrafine cement sealing grout according to the set weight proportions;

[0115] (3) Mix urease-producing bacterial solution and ultrafine cement sealing grout in a volume ratio of 4:1 to obtain the sealing agent.

[0116] Example 4

[0117] This embodiment provides a sealing agent for treating annular pressure. The sealing agent includes urease solution and ultrafine cement sealing slurry, and the volume ratio of urease solution to ultrafine cement sealing slurry is 3:1. The plastic viscosity of the sealing agent is 20 MPa·s.

[0118] Specifically, the urease solution comprises urease, urea, and deionized water, and the concentration of the urease is 6.0 g / L; the concentration of the urea is 0.10 mol / L.

[0119] The ultrafine cement sealing grout comprises the following components by weight:

[0120]

[0121]

[0122] In this embodiment, the average particle size D of the ultrafine cementitious substrate material 50It has a diameter of 25 μm and a specific surface area of ​​1500 m². 2 / kg.

[0123] This embodiment also provides a method for preparing the above-mentioned blocking agent, the preparation method comprising the following steps:

[0124] (1) Mix urease, urea and deionized water to prepare urease solution, wherein the concentration of urease in the urease solution is 6.0 g / L and the concentration of urea is 0.10 mol / L;

[0125] (2) Prepare ultrafine cement sealing grout according to the set weight proportions;

[0126] (3) Mix urease solution and ultrafine cement sealing grout in a volume ratio of 3:1 to obtain the sealing agent.

[0127] Comparative Example 1

[0128] This comparative example provides a sealing agent for treating annular pressure and its preparation method. Except for changing the volume ratio of urease-producing bacteria solution and ultrafine cement sealing slurry to 1:1, and increasing the plastic viscosity of the sealing agent to 40 MPa·s, the other steps and conditions are the same as in Example 1, so they will not be described in detail here.

[0129] Comparative Example 2

[0130] This comparative example provides a plugging agent for treating annular pressure and its preparation method. Except for replacing the ultrafine cement base material with G-grade oil well cement and removing calcium oxalate (organic early strength agent) and microsilica (active material), the other steps and conditions are the same as in Example 1, so they will not be described in detail here.

[0131] Comparative Example 3

[0132] This comparative example provides a sealing agent for treating annular pressure and its preparation method. The method is a traditional cement slurry for treating annular pressure, which only includes ultrafine cement sealing slurry and does not contain urease solution or urease-producing bacteria solution. The plastic viscosity of the sealing agent increases to 60 MPa·s. The remaining steps and conditions are the same as in Example 1, so they will not be described in detail here.

[0133] Performance testing

[0134] Test on the sealing effect of the plugging agent on the annular cement ring: The thickening time of the plugging agents obtained in Examples 1-4 and Comparative Examples 1-3 at 26°C, as well as their sealing and reinforcement effects on sand columns (simulating annular cement rings), are shown in Table 1 below.

[0135] Table 1

[0136]

[0137] As shown in Table 1:

[0138] (A) Regarding the thickening time, the thickening time of the plugging agents obtained in Examples 1-4 and Comparative Examples 1-3 is related to the mixing volume ratio of the plugging agents. The higher the proportion of the ultrafine cement slurry system, the shorter the thickening time of the plugging agent. However, the thickening time is not directly related to the annular pressurized plugging effect.

[0139] (B) Regarding compressive strength, the sealing fluid is injected into the sand column to improve its compressive strength. Examples 1-4 and Comparative Examples 1-3 all improve the compressive strength of the sand column, and the compressive strength values ​​of Examples 2 and 4 are greater than those of Comparative Example 3, indicating that the sealing agent provided by this invention has a stronger reinforcement effect than the ultrafine cement used in traditional annular pressure treatment.

[0140] (C) Regarding the rate of change in permeability and shear bond strength, these two parameters directly describe the cement stone's ability to prevent fluid migration at the interface and within the cement stone, and directly indicate the annular pressure treatment capability of the sealing agent. A comparison of Examples 1-4 with Comparative Example 1 shows that, under the same injection pressure conditions, lower plastic viscosity allows the sealing fluid to produce a better sealing effect. This is because lower plastic viscosity results in less friction, allowing the sealing fluid to enter smaller pores within the sand and reinforce small-diameter pores. A comparison of Examples 1-4 with Comparative Example 2 shows that organic early-strength agents, active materials, and ultrafine cement-based materials can improve the sealing effect. A comparison of Examples 1-4 with Comparative Example 3 shows that calcium carbonate produced under the induction of urease solution or urease-producing bacterial solution can effectively fill and seal small-sized pores and micro-cracks in the sand column, reducing permeability, while simultaneously improving interfacial bond strength, i.e., improving the density and anti-channeling ability of the cement annulus.

[0141] Furthermore, the specific treatment methods for treating annular pressure using the plugging agent provided by this invention are as follows: (1) directly injecting the plugging agent into the annulus through a phased circulation from the wellhead; (2) first directly injecting urease active liquid, and then injecting ultrafine cement plugging slurry in batches. Both of the above methods can produce good treatment effects for annular pressure.

[0142] Therefore, the sealing agent provided by the present invention induces the generation of carbonate ions through urease active liquid, and provides calcium ions with the help of calcium-containing early strength agent in ultrafine cement sealing slurry. The carbonate ions combine with calcium ions to form calcium carbonate deposits. Subsequently, calcium carbonate crystals continuously accumulate, gradually compressing the internal pore space of the cement ring body during the treatment of annular pressure. Macroscopically, this is manifested as filling of cement ring cracks, reducing permeability, and increasing interfacial bonding strength.

[0143] Furthermore, by limiting the volume ratio of urease active liquid to ultrafine cement sealing slurry within a reasonable range, this invention maintains the solid content in the sealing agent at a low level and has low plastic viscosity. This facilitates the full injection of the sealing agent into the microcracks of the cement annulus, reduces the annular pumping pressure and construction costs, and avoids the situation where the sealing agent cannot enter the microcracks due to filtration loss caused by the presence of solid particles. Thus, it effectively seals small-sized microcracks and improves the treatment effect of annular pressure.

[0144] Furthermore, the sealing agent provided by this invention can be cured at room temperature, thus enabling the treatment of annular pressure caused by cement sheath integrity failure in shallow formations. At the same time, the sealing agent is environmentally friendly and its environmental performance is significantly better than that of traditional resin-based sealing agents, which is conducive to large-scale promotion and application.

[0145] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A sealing agent for treating annular pressure, characterized in that, The sealing agent is composed of urease active liquid and ultrafine cement sealing grout; The urease active solution includes urease-producing bacterial solution and / or urease solution, used to induce the production of carbonate ions; The ultrafine cement sealing grout is composed of the following components by weight: 100 parts of ultrafine cementitious base material; 5-20 parts of highly active material; 1-6 parts of calcium-containing early-strength agent; Organic early-strength agent 0.05-1 part; Dispersant 0.5-2 parts; Defoamer 0.1-1 part; 30-50 parts deionized water; And the average particle size D of the ultrafine cementitious substrate material 50 ≤30μm; The volume ratio of the urease active liquid to the ultrafine cement sealing grout is (2-4):1; The plastic viscosity of the plugging agent is 5-30 mPa·s.

2. The sealing agent according to claim 1, characterized in that, The urease-producing bacterial solution includes urease-producing bacteria, an inducer, and deionized water.

3. The sealing agent according to claim 1, characterized in that, The urease solution includes urease, an inducer, and deionized water.

4. The sealing agent according to claim 2, characterized in that, The urease-producing bacteria include Bacillus pasteurellii, and the bacterial cell density OD 600 It ranges from 0.5 to 1.

0.

5. The sealing agent according to claim 3, characterized in that, The concentration of the urease is 3.0-10.0 g / L.

6. The sealing agent according to claim 2 or 3, characterized in that, The inducing agent includes urea, and the concentration of the urea is 0.05-0.15 mol / L.

7. The sealing agent according to claim 1, characterized in that, The specific surface area of ​​the ultrafine cementitious substrate material is ≥1000 m². 2 / kg.

8. The sealing agent according to claim 1, characterized in that, The highly active material includes any one or a combination of at least two of sulfoaluminate, microsilica, or metakaolin fly ash.

9. The sealing agent according to claim 1, characterized in that, The calcium-containing early-strength agent includes any one or a combination of at least two of calcium chloride, calcium sulfate, or calcium nitrate.

10. The sealing agent according to claim 1, characterized in that, The organic early-strength agent includes calcium oxalate and / or triethanolamine.

11. A method for preparing the plugging agent according to any one of claims 1-10, characterized in that, The preparation method includes the following steps: (1) Preparation of urease active solution; (2) Prepare ultrafine cement sealing grout; (3) Mix urease active solution and ultrafine cement sealing grout to obtain sealing agent; Steps (1) and (2) are not in any particular order.

12. The preparation method according to claim 11, characterized in that, The urease active solution in step (1) includes urease-producing bacterial solution and / or urease solution.

13. The preparation method according to claim 12, characterized in that, The method for preparing the urease-producing bacterial culture includes the following steps: (a) Yeast extract, sodium chloride and inducer were added to deionized water and mixed evenly to prepare fermentation medium; (b) Sterilize the fermentation medium; (c) Inoculate the fermentation medium with urease-producing bacteria and culture it under stirring conditions to obtain a urease-producing bacterial solution.

14. The preparation method according to claim 13, characterized in that, The concentration of yeast extract in the fermentation medium in step (a) is 15-25 g / L.

15. The preparation method according to claim 13, characterized in that, The concentration of sodium chloride in the fermentation medium in step (a) is 4-6 g / L.

16. The preparation method according to claim 13, characterized in that, The concentration of the inducer in the fermentation medium in step (a) is 0.05-0.15 mol / L, and the inducer includes urea.

17. The preparation method according to claim 13, characterized in that, The pH of the fermentation medium in step (a) is 7-9.

18. The preparation method according to claim 13, characterized in that, The sterilization temperature in step (b) is 115-125℃.

19. The preparation method according to claim 13, characterized in that, The sterilization process in step (b) takes 20-40 minutes.

20. The preparation method according to claim 13, characterized in that, The stirring speed in step (c) is 100-140 rpm.

21. The preparation method according to claim 13, characterized in that, The culture temperature in step (c) is 25-35℃.

22. The preparation method according to claim 13, characterized in that, The incubation time in step (c) is 12-24 hours.

23. The preparation method according to claim 11, characterized in that, The preparation method includes the following steps: (1) Preparation of urease active solution; the urease active solution includes urease-producing bacterial solution and / or urease solution, and the preparation method of the urease-producing bacterial solution is as follows: (a) Yeast extract, sodium chloride and urea are added to deionized water and mixed evenly to prepare a fermentation medium with a pH of 7-9; the concentration of yeast extract in the fermentation medium is 15-25 g / L, the concentration of sodium chloride is 4-6 g / L and the concentration of urea is 0.05-0.15 mol / L. (b) Sterilize the fermentation medium at 115-125℃ for 20-40 minutes; (c) Inoculate the fermentation medium with urease-producing bacteria, and culture it under stirring conditions of 100-140 rpm, at a temperature of 25-35℃, for 12-24 h to obtain urease-producing bacterial solution; (2) Prepare ultrafine cement sealing grout; (3) Mix urease active solution and ultrafine cement sealing grout in a volume ratio of (2-4):1 to obtain a sealing agent; Steps (1) and (2) are not in any particular order.

24. An application of the plugging agent as described in any one of claims 1-10, characterized in that, The sealing agent is used to treat annular pressure.

25. The application according to claim 24, characterized in that, The treatment of annular pressure includes any one of the following two methods: (A) Directly injecting plugging agent into the annulus through a phased circulation process from the wellhead; (B) First, inject urease active solution directly, and then inject ultrafine cement sealing grout in batches.

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