Plugging agent for treating annulus pressure as well as preparation method and application thereof

Abstract

The invention provides a plugging agent for treating annulus pressure as well as a preparation method and application of the plugging agent. The plugging agent comprises urease active liquid and superfine cement plugging slurry, the urease active liquid comprises urease-producing bacterium liquid and / or urease liquid and is used for inducing to produce carbonate radicals; the superfine cement plugging slurry comprises a superfine cement base material and a calcium-containing early strength agent, wherein the average particle size D50 of the superfine cement base material is less than or equal to 30 microns; the volume ratio of the urease active liquid to the superfine cement plugging slurry is (2-4): 1; and the plastic viscosity of the plugging agent is 5-30 mpa * s. The blocking agent provided by the invention effectively blocks small-size micro-cracks, improves the treatment effect of annulus pressure, improves the environmental protection property, reduces the production and construction operation cost, and is beneficial to large-scale popularization and application.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and gas exploitation, and relates to a plugging agent for controlling annular space pressure, and in particular to a plugging agent for controlling annular space pressure, and a preparation method and application thereof. Background Art

[0002] With the increase in oil and gas production, the annular pressure of oil and gas wells is becoming more and more common, posing a serious threat to safe production. During the exploitation of oil and gas wells, the annular space between the layers of casing in the wellbore needs to be filled with cement to form several annular closed barriers composed of multiple layers of casing and cement. While sealing, the annular barrier can also prevent the infiltration of underground oil, gas, water and other fluids, thereby ensuring safe construction and exploitation in the later stage.

[0003] The main causes of annular pressure include: (1) the integrity of the cement sheath is damaged; (2) the cement sheath fails to bond with the casing or the cement sheath fails to bond with the formation. The existence 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, and the cost of wellhead annular pressure monitoring and pressure relief is increasing year by year. In severe cases, it may even cause blowout accidents.

[0004] At present, the main means of controlling annular pressure is to overhaul oil and gas wells and squeeze cement, resin and other plugging materials into the annulus to re-block fluid channels such as micro-cracks in the cement annulus. However, since the cracks in the cement annulus are very small, the materials containing the solid phase cannot fully enter and fill them. The construction of squeezing cement into the annulus is difficult, dangerous, and has a low success rate. Therefore, how to develop a new plugging agent system with excellent performance has become the key to effectively solving the problem of annular pressure.

[0005] CN113930200A discloses a sealant for treating annular pressure, and its preparation method and application, wherein the sealant comprises a composite resin, a curing agent, a toughening agent and a viscosity reducer. The sealant is squeezed from the ground annulus into the annulus of an oil and gas well and cured to seal the micro-cracks of the cement annulus, so that the annulus of the oil and gas well can be effectively sealed to solve the problem of casing annular pressure. However, the sealant has a high viscosity (1000-1500mpa·s), and cannot effectively seal small-sized micro-cracks. In addition, the sealant has problems such as poor environmental protection, high production and construction costs, etc.

[0006] In addition, as an emerging geological engineering reinforcement method, microbial induced calcium carbonate precipitation (MICP) technology is gradually emerging and becoming the focus of various research fields because of its environmental protection, low energy consumption, pollution-free, high efficiency and fast characteristics. MICP produces crystalline and non-crystalline inorganic compounds through metabolism, which play a filling and bonding role in the soil, further improving the performance of soil and concrete.

[0007] CN109594552A discloses a method for microbial solidification fiber reinforcement combined with modified sand. In view of the increased brittleness of sand after microbial solidification, basalt fiber, carbon fiber and steel fiber are respectively added into the MICP technology to improve the brittleness of the sand after solidification, and improve its residual strength and toughness. CN111749227A discloses a method for microbial combined with rubber material to induce carbonate precipitation, by adding rubber particles into the MICP technology to improve the anti-liquefaction performance of solidified sand. However, since the MICP technology has not yet been applied to the field of cementing, there are still many problems in both indoor and field tests that need to be studied in depth, the most important of which is the application in the management of annular pressure.

[0008] It can be seen that how to provide a plugging agent and a preparation method for controlling annular pressure based on microbial-induced calcium carbonate precipitation technology, especially to effectively plug small-sized microcracks, improve the control effect of annular pressure, while improving environmental protection and reducing production and construction costs, has become a problem that technical personnel in this field urgently need to solve. Summary of the invention

[0009] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a plugging agent for controlling annular space pressure, and a preparation method and application thereof. The plugging agent effectively blocks small-sized microcracks, improves the control effect of annular space pressure, and at the same time enhances environmental protection, reduces production and construction costs, and is conducive to large-scale promotion and application.

[0010] To achieve this object, the present invention adopts the following technical solutions:

[0011] In a first aspect, the present invention provides a plugging agent for controlling annular space pressure, wherein the plugging agent comprises urease active liquid and ultrafine cement plugging slurry.

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

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

[0014] The volume ratio of the urease active solution to the ultrafine cement sealing slurry 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 is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0015] The plastic viscosity of the plugging agent is 5-30 MPa·s, for example, 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, and other unlisted values ​​within the numerical range are also applicable.

[0016] The plugging agent provided by the present invention induces the production of carbonate ions through urease active liquid, and provides calcium ions with the help of calcium-containing early strength agent in ultrafine cement plugging slurry. The carbonate ions combine with calcium ions to form calcium carbonate deposition, and calcium carbonate crystals are subsequently continuously aggregated. In the process of managing annular pressure, the pore space inside the cement sheath body is gradually compressed, which is manifested macroscopically as filling of cement sheath cracks, reduced permeability, and improved interface bonding strength.

[0017] In addition, the present invention limits the volume ratio of urease active liquid and ultrafine cement plugging slurry within a reasonable range, that is, the solid content in the plugging agent is maintained at a low level, and the plastic viscosity is small, which is conducive to the full squeezing of the plugging agent into the microcracks of the cement ring, reduces the annular space pumping pressure and construction operation costs, and avoids the situation in which the plugging agent cannot enter the microcracks due to the loss phenomenon caused by the presence of solid phase particles, thereby forming an effective plugging for small-sized microcracks and improving the control effect of annular space pressure.

[0018] The plugging agent provided by the present invention can be solidified at room temperature, and can then be used to treat annular pressure caused by cement ring integrity failure in shallow strata. At the same time, the plugging agent is environmentally friendly, improves environmental protection, and is conducive to 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 pasteurianus, and the cell density OD 600 It 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, and other unlisted values ​​within the numerical range are also applicable.

[0022] Preferably, the concentration of urease is 3.0-10.0 g / L, for example, 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, and other unlisted values ​​within the numerical range are also applicable.

[0023] Preferably, the inducer includes 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, and other unlisted values ​​within the numerical range are also applicable.

[0024] Preferably, the ultrafine cement plugging slurry comprises the following components in parts by weight:

[0025]

[0026] Among them, the weight proportion of the highly active material is 5-20 parts, for example, it can be 5 parts, 6 parts, 8 parts, 10 parts, 12 parts, 14 parts, 16 parts, 18 parts or 20 parts; the weight proportion of the calcium-containing early strength agent is 1-6 parts, for example, it can be 1 part, 2 parts, 3 parts, 4 parts, 5 parts or 6 parts; the weight proportion of the organic early strength agent is 0.05-1 part, for example, it can be 0.05 parts, 0.1 parts, 0.2 parts, 0.3 parts, 0.4 parts, 0.5 parts, 0.6 parts, 0.7 parts, 0.8 parts, 0.9 parts or 1 parts; the weight proportion of the dispersant is 0.5-2 parts, for example, it can be 0.5 parts , 0.6 parts, 0.8 parts, 1 parts, 1.2 parts, 1.4 parts, 1.6 parts, 1.8 parts or 2 parts; the weight proportion of the defoaming agent is 0.1-1 parts, for example, it can be 0.1 parts, 0.2 parts, 0.3 parts, 0.4 parts, 0.5 parts, 0.6 parts, 0.7 parts, 0.8 parts, 0.9 parts or 1 parts; the weight proportion of the deionized water is 30-50 parts, for example, it can be 30 parts, 32 parts, 34 parts, 36 parts, 38 parts, 40 parts, 42 parts, 44 parts, 46 parts, 48 ​​parts or 50 parts, but is not limited to the listed values, and other unlisted values ​​within the numerical range are equally applicable.

[0027] Preferably, the specific surface area of ​​the ultrafine cement base material is ≥1000m 2 / kg, for example, it can 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 is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0028] In the present invention, the high-activity material refers to an oil well cement admixture with high hydration activity, which can shorten the initial setting time of cement slurry and improve the early strength of cement paste under the activation of early strength agent.

[0029] Preferably, the high-activity material comprises any one or a combination of at least two of sulphoaluminate, microsilica or kaolin fly ash. Typical but non-limiting combinations include a combination of sulphoaluminate and microsilica, a combination of microsilica and kaolin fly ash, a combination of sulphoaluminate and metakaolin fly ash, or a combination of sulphoaluminate, microsilica and metakaolin fly ash.

[0030] In the present invention, the highly active material can significantly accelerate the deposition of calcium ions, increase the total mass of deposited calcium carbonate, and can also enable the microbial-induced calcium carbonate deposition process to continue when the amount of the reaction solution is increased.

[0031] Preferably, the calcium-containing early strength agent includes any one of calcium chloride, calcium sulfate or calcium nitrate, or a combination of at least two of them. 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 the ultrafine cement plugging slurry and improve the compressive strength of the cement paste; on the other hand, the calcium-containing early strength agent provides a calcium source for the urease active liquid to maintain 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 paste; on the other hand, C, H, O, and N are its main components, which can provide urease-producing bacteria with additional nutrients such as carbon source and nitrogen source required for growth, thereby better promoting bacterial growth, increasing urease activity and calcium carbonate production, and enhancing the cement sheath reinforcement and anti-seepage effects.

[0035] In the present invention, the dispersant and defoamer are both plugging agent components conventionally used in the art, and as long as they can achieve the corresponding dispersing and defoaming functions, the specific types or models of the dispersant and defoamer are not particularly limited herein.

[0036] In a second aspect, the present invention provides a method for preparing the plugging agent according to the first aspect, the preparation method comprising the following steps:

[0037] (1) preparing urease active solution;

[0038] (2) Prepare ultra-fine cement plugging slurry;

[0039] (3) Mixing urease active liquid and ultrafine cement plugging slurry to obtain a plugging agent.

[0040] There is no particular order in which steps (1) and (2) are performed.

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

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

[0043] (a) adding yeast extract, sodium chloride and an inducer into deionized water respectively and mixing them evenly to prepare a fermentation medium;

[0044] (b) sterilizing the fermentation medium;

[0045] (c) inoculating urease-producing bacteria into a fermentation medium, and culturing the medium under stirring to obtain a urease-producing bacterial solution.

[0046] Preferably, the concentration of the yeast extract in the fermentation medium in step (a) is 15-25 g / L, for example, 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, and other values ​​not listed within the numerical 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, 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, and other values ​​not listed within the numerical range are also applicable.

[0048] Preferably, the concentration of the inducer in the fermentation medium of 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, and other values ​​not listed within the numerical 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, 7, 7.2, 7.4, 7.6, 7.8, 8, 8.2, 8.4, 8.6, 8.8 or 9, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0051] Preferably, the temperature of the sterilization treatment 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, and other unlisted values ​​within the numerical range are also applicable.

[0052] Preferably, the sterilization treatment 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 is not limited to the listed values, and other unlisted values ​​within the numerical 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 is not limited to the listed values, and other unlisted values ​​within the numerical 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 is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0055] Preferably, the culturing time in step (c) is 12-24 h, for example, 12 h, 14 h, 16 h, 18 h, 20 h, 22 h or 24 h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0056] As a preferred technical solution of the second aspect of the present invention, the preparation method comprises the following steps:

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

[0058] (a) adding yeast extract, sodium chloride and urea to deionized water respectively, and mixing them evenly to prepare a fermentation medium with a pH value 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) sterilizing the fermentation medium at 115-125° C. for 20-40 min;

[0060] (c) inoculating urease-producing bacteria into a fermentation medium, culturing under stirring conditions of 100-140 rpm, at a temperature of 25-35° C., for 12-24 hours, to obtain a urease-producing bacterial solution;

[0061] (2) Prepare ultra-fine cement plugging slurry;

[0062] (3) The urease active liquid and the ultrafine cement plugging slurry are mixed in a volume ratio of (2-4):1 to obtain a plugging agent.

[0063] There is no particular order in which steps (1) and (2) are performed.

[0064] In a third aspect, the present invention provides a use of the plugging agent as described in the first aspect, wherein the plugging agent is used to control annular space pressure.

[0065] Preferably, the annular pressure control comprises any one of the following two methods:

[0066] (A) Directly inject the plugging agent from the wellhead into the annulus in stages;

[0067] (B) First, directly inject urease active liquid, and then inject ultra-fine cement sealing slurry in batches.

[0068] In method (A), urease active liquid is combined with ultrafine cement plugging slurry to obtain a plugging agent, wherein the ultrafine cement plugging slurry is used as a matrix material for grouting and plugging, and is used to fill the pores between cement hydration products; the urease active liquid has a small plastic viscosity and can enter and plug 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 between microcracks, small-diameter pores and sand particles, which plays a role in preliminarily consolidating the cement sheath body and interface.

[0070] The numerical range described in the present invention not only includes the point values ​​listed above, but also includes any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0071] Compared with the prior art, the present invention has the following beneficial effects:

[0072] (1) The plugging agent provided by the present invention induces the production of carbonate ions through urease active liquid, and provides calcium ions with the help of calcium-containing early strength agent in ultrafine cement plugging slurry. Carbonate ions combine with calcium ions to form calcium carbonate deposition. Subsequently, calcium carbonate crystals continue to aggregate, and gradually compress the pore space inside the cement ring body during the process of treating annular pressure. Macroscopically, the cement ring cracks are filled, the permeability is reduced, and the interface bonding strength is improved;

[0073] (2) The present invention limits the volume ratio of urease active liquid and ultrafine cement plugging slurry within a reasonable range, that is, the solid content in the plugging agent is maintained at a low level, and the plastic viscosity is small, which is conducive to the full injection of the plugging agent into the microcracks of the cement ring, reducing the annular pumping pressure and construction operation costs, and avoiding the situation where the plugging agent cannot enter the microcracks due to the presence of solid particles. The phenomenon of filtration loss is avoided, thereby effectively plugging small-sized microcracks and improving the treatment effect of annular pressure.

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

[0075] The technical solution of the present invention is further illustrated below through specific implementation methods.

[0076] Example 1

[0077] This embodiment provides a plugging agent for controlling annular pressure, wherein the plugging agent comprises urease-producing bacteria liquid and ultrafine cement plugging slurry, wherein the volume ratio of the urease-producing bacteria liquid to the ultrafine cement plugging slurry is 3:1, and the plastic viscosity of the plugging 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 includes Bacillus pasteurianus, and the bacterial cell density OD 600 is 0.8; the concentration of the urea is 0.10 mol / L.

[0079] The ultrafine cement plugging slurry comprises the following components in parts by weight:

[0080]

[0081] In this embodiment, the average particle size D of the ultrafine cement base material is 50 The surface area is 25 μm and the specific surface area is 1500 m 2 / kg.

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

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

[0084] (a) adding yeast extract, sodium chloride and urea to deionized water respectively, and mixing them uniformly to prepare a fermentation medium with a pH value of 8; the concentration of yeast extract in the fermentation medium is 20 g / L, the concentration of sodium chloride is 5 g / L, and the concentration of urea is 0.10 mol / L;

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

[0086] (c) inoculating urease-producing bacteria into a fermentation medium, culturing under stirring conditions of 120 rpm and a temperature of 30° C. for 18 h to obtain a urease-producing bacterial solution;

[0087] (2) preparing ultrafine cement plugging slurry according to the set weight proportion;

[0088] (3) The urease-producing bacteria solution and the ultrafine cement plugging slurry are mixed in a volume ratio of 3:1 to obtain a plugging agent.

[0089] Example 2

[0090] This embodiment provides a plugging agent for controlling annular pressure, wherein the plugging agent comprises urease-producing bacteria liquid and ultrafine cement plugging slurry, wherein the volume ratio of the urease-producing bacteria liquid to the ultrafine cement plugging slurry is 2:1, and the plastic viscosity of the plugging 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 includes Bacillus pasteurianus, and the bacterial cell density OD 600 is 1.0; the concentration of the urea is 0.15 mol / L.

[0092] The ultrafine cement plugging slurry comprises the following components in parts by weight:

[0093]

[0094] In this embodiment, the average particle size D of the ultrafine cement base material is 50 The surface area is 30 μm and the specific surface area is 1000 m 2 / kg.

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

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

[0097] (a) adding yeast extract, sodium chloride and urea to deionized water respectively, and mixing them uniformly to prepare a fermentation medium with a pH value of 7; the concentration of yeast extract in the fermentation medium is 25 g / L, the concentration of sodium chloride is 6 g / L, and the concentration of urea is 0.15 mol / L;

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

[0099] (c) inoculating urease-producing bacteria into a fermentation medium, culturing the medium under stirring conditions of 100 rpm at a temperature of 25° C. for 24 h to obtain a urease-producing bacterial solution;

[0100] (2) preparing ultrafine cement plugging slurry according to the set weight proportion;

[0101] (3) The urease-producing bacteria solution and the ultrafine cement plugging slurry are mixed in a volume ratio of 2:1 to obtain a plugging agent.

[0102] Example 3

[0103] This embodiment provides a plugging agent for controlling annular pressure, wherein the plugging agent comprises urease-producing bacteria liquid and ultrafine cement plugging slurry, wherein the volume ratio of the urease-producing bacteria liquid to the ultrafine cement plugging slurry is 4:1, and the plastic viscosity of the plugging 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 includes Bacillus pasteurianus, and the bacterial cell density OD 600 is 0.5; the concentration of the urea is 0.05 mol / L.

[0105] The ultrafine cement plugging slurry comprises the following components in parts by weight:

[0106]

[0107]

[0108] In this embodiment, the average particle size D of the ultrafine cement base material is 50 The surface area is 20 μm and the specific surface area is 2000 m 2 / kg.

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

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

[0111] (a) adding yeast extract, sodium chloride and urea to deionized water respectively, and mixing them uniformly to prepare a fermentation medium with a pH value of 9; the concentration of yeast extract in the fermentation medium is 15 g / L, the concentration of sodium chloride is 4 g / L, and the concentration of urea is 0.05 mol / L;

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

[0113] (c) inoculating urease-producing bacteria into a fermentation medium, culturing under stirring conditions of 140 rpm and a temperature of 35° C. for 12 h to obtain a urease-producing bacterial solution;

[0114] (2) preparing ultrafine cement plugging slurry according to the set weight proportion;

[0115] (3) The urease-producing bacteria liquid and the ultrafine cement plugging slurry are mixed in a volume ratio of 4:1 to obtain a plugging agent.

[0116] Example 4

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

[0118] Specifically, the urease solution includes 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 plugging slurry comprises the following components in parts by weight:

[0120]

[0121]

[0122] In this embodiment, the average particle size D of the ultrafine cement base material is 50The surface area is 25 μm and the specific surface area is 1500 m 2 / kg.

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

[0124] (1) mixing urease, urea and deionized water to prepare a 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) preparing ultrafine cement plugging slurry according to the set weight proportion;

[0126] (3) Urease solution and ultrafine cement plugging slurry are mixed in a volume ratio of 3:1 to obtain a plugging agent.

[0127] Comparative Example 1

[0128] This comparative example provides a plugging agent for controlling annular pressure and a preparation method thereof. Except that the volume ratio of urease-producing bacterial solution and ultrafine cement plugging slurry is changed to 1:1, and the plastic viscosity of the plugging agent is increased to 40 MPa·s, the remaining steps and conditions are the same as those in Example 1, and thus are not described in detail here.

[0129] Comparative Example 2

[0130] This comparative example provides a plugging agent for controlling annular pressure and a preparation method thereof. Except for changing the ultrafine cement base material to G-grade oil well cement and removing calcium oxalate (organic early strength agent) and microsilicon (active material), the remaining steps and conditions are the same as those in Example 1, so they are not repeated here.

[0131] Comparative Example 3

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

[0133] Performance Testing

[0134] Test on the plugging effect of plugging agent on annulus 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 the plugging and reinforcement effects on the sand column (simulating the annulus cement ring) are shown in Table 1 below.

[0135] Table 1

[0136]

[0137] From Table 1, we can see that:

[0138] (A) In terms of 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 has no direct correlation with the annular pressure plugging effect.

[0139] (B) In terms of compressive strength, the plugging liquid is injected into the sand column to improve the compressive strength of the sand column. Examples 1-4 and Comparative Examples 1-3 can 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 plugging agent provided by the present invention has a stronger reinforcement effect than the ultrafine cement for traditional annular pressure treatment.

[0140] (C) In terms of permeability change rate and shear bonding strength, the above two parameters can directly describe the ability of cement stone to prevent fluid migration at the interface and inside the cement stone, and directly indicate the annular pressure management ability of the plugging agent. The comparison of Examples 1-4 and Comparative Example 1 shows that under the same injection pressure conditions, lower plastic viscosity can make the plugging fluid produce better plugging effect, because lower plastic viscosity has less friction, which can make the plugging fluid enter smaller pores in the sand and reinforce small pores. The comparison of Examples 1-4 and Comparative Example 2 shows that organic early strength agents, active materials, and ultrafine cement-based materials can improve the plugging effect. The comparison of Examples 1-4 and Comparative Example 3 shows that the calcium carbonate produced under the induction of urease solution or urease-producing bacteria solution can effectively fill and plug small-sized pores and micro-gaps in the sand column, reduce permeability, and at the same time improve the interface bonding strength, that is, improve the density and channeling ability of the cement ring.

[0141] In addition, the specific treatment methods of the plugging agent provided by the present invention for treating annular pressure are divided into the following two types: (1) directly injecting the plugging agent from the wellhead into the annular space in stages; (2) first directly injecting urease active liquid, and then injecting ultrafine cement plugging slurry in batches. Both of the above methods can produce better annular pressure treatment effects.

[0142] It can be seen that the plugging agent provided by the present invention induces the production of carbonate ions through the urease active liquid, and provides calcium ions with the help of the calcium-containing early strength agent in the ultrafine cement plugging slurry. The carbonate ions combine with the calcium ions to form calcium carbonate deposition, and the subsequent calcium carbonate crystals continue to aggregate. In the process of controlling the annular pressure, the pore space inside the cement ring body is gradually compressed, which is manifested macroscopically as the filling of cement ring cracks, the reduction of permeability, and the improvement of interface bonding strength.

[0143] In addition, the present invention limits the volume ratio of urease active liquid and ultrafine cement plugging slurry within a reasonable range, that is, the solid content in the plugging agent is maintained at a low level, and the plastic viscosity is small, which is conducive to the full squeezing of the plugging agent into the microcracks of the cement ring, reduces the annular space pumping pressure and construction operation costs, and avoids the situation in which the plugging agent cannot enter the microcracks due to the loss phenomenon caused by the presence of solid phase particles, thereby forming an effective plugging for small-sized microcracks and improving the control effect of annular space pressure.

[0144] Furthermore, the plugging agent provided by the present invention can be solidified at room temperature, and can be used to treat annular pressure caused by failure of cement ring integrity in shallow formations. At the same time, the plugging agent is environmentally friendly and has significantly better environmental protection than traditional resin plugging agents, which is conducive to large-scale promotion and application.

[0145] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is 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 in the protection scope of the present invention.

Claims

1. A plugging agent for treating annular pressure, characterized in that: The plugging agent includes urease active liquid and ultrafine cement plugging slurry; The urease active solution includes urease-producing bacteria solution and / or urease solution, which is used to induce the production of carbonate; The ultrafine cement plugging slurry comprises an ultrafine cement base material and a calcium-containing early strength agent, and the average particle size D of the ultrafine cement base material is 50 ≤30μm; The volume ratio of the urease active liquid to the ultrafine cement plugging slurry is (2-4):1; The plastic viscosity of the plugging agent is 5-30 mpa·s.

2. The plugging agent according to claim 1, characterized in that: The urease-producing bacterial solution comprises urease-producing bacteria, an inducer and deionized water; Preferably, the urease solution comprises urease, an inducer and deionized water; Preferably, the urease-producing bacteria include Bacillus pasteurianus, and the cell density OD 600 0.5-1.0; Preferably, the concentration of urease is 3.0-10.0 g / L; Preferably, the inducer comprises urea, and the concentration of the urea is 0.05-0.15 mol / L.

3. The plugging agent according to claim 1 or 2, characterized in that: The ultrafine cement plugging slurry comprises the following components in parts by weight:

4. The plugging agent according to claim 3, characterized in that: The specific surface area of ​​the ultrafine cement base material is ≥1000m 2 / kg; Preferably, the highly active material comprises any one or a combination of at least two of sulphoaluminate, microsilica or metakaolin fly ash; Preferably, the calcium-containing early strength agent includes any one of calcium chloride, calcium sulfate or calcium nitrate, or a combination of at least two thereof; Preferably, the organic early strength agent comprises calcium oxalate and / or triethanolamine.

5. A method for preparing the plugging agent according to any one of claims 1 to 4, characterized in that: The preparation method comprises the following steps: (1) preparing urease active solution; (2) Prepare ultra-fine cement plugging slurry; (3) mixing urease active liquid and ultrafine cement plugging slurry to obtain a plugging agent; There is no particular order in which steps (1) and (2) are performed.

6. The preparation method according to claim 5, characterized in that: The urease active solution in step (1) includes urease-producing bacteria solution and / or urease solution; Preferably, the method for preparing the urease-producing bacterial liquid comprises the following steps: (a) adding yeast extract, sodium chloride and an inducer into deionized water respectively and mixing them evenly to prepare a fermentation medium; (b) sterilizing the fermentation medium; (c) inoculating urease-producing bacteria into a fermentation medium, and culturing the medium under stirring to obtain a urease-producing bacterial solution.

7. The preparation method according to claim 6, characterized in that: The concentration of yeast extract in the fermentation medium of step (a) is 15-25 g / L; Preferably, the concentration of sodium chloride in the fermentation medium in step (a) is 4-6 g / L; Preferably, the concentration of the inducer in the fermentation medium in step (a) is 0.05-0.15 mol / L, and the inducer comprises urea; Preferably, the pH value of the fermentation medium in step (a) is 7-9; Preferably, the temperature of the sterilization treatment in step (b) is 115-125°C; Preferably, the sterilization treatment time in step (b) is 20-40 minutes; Preferably, the stirring speed in step (c) is 100-140 rpm; Preferably, the culture temperature in step (c) is 25-35°C; Preferably, the culturing time in step (c) is 12-24 hours.

8. The preparation method according to any one of claims 5 to 7, characterized in that: The preparation method comprises the following steps: (1) Preparing a urease active solution; the urease active solution includes a urease-producing bacterial solution and / or a urease solution, and the preparation method of the urease-producing bacterial solution is as follows: (a) adding yeast extract, sodium chloride and urea to deionized water respectively, and mixing them evenly to prepare a fermentation medium with a pH value 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) sterilizing the fermentation medium at 115-125° C. for 20-40 min; (c) inoculating urease-producing bacteria into a fermentation medium, culturing under stirring conditions of 100-140 rpm, at a temperature of 25-35° C., for 12-24 hours, to obtain a urease-producing bacterial solution; (2) Prepare ultra-fine cement plugging slurry; (3) mixing urease active liquid and ultrafine cement plugging slurry in a volume ratio of (2-4):1 to obtain a plugging agent; There is no particular order in which steps (1) and (2) are performed.

9. A use of the plugging agent according to any one of claims 1 to 4, characterized in that: The plugging agent is used to control annular space pressure.

10. The use according to claim 9, characterized in that: The annular pressure control method includes any one of the following two methods: (A) Directly inject the plugging agent from the wellhead into the annulus in stages; (B) First, directly inject urease active liquid, and then inject ultra-fine cement sealing slurry in batches.

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