High-temperature profile control plugging agent for steam injection well

Abstract

The invention discloses a high-temperature profile control plugging agent for a steam injection well. The high-temperature profile control plugging agent for the steam injection well comprises the following components in percentage by mass: 5-10% of aluminum sulfate; 10%-15% of calcium sulfide; 5%-10% of bentonite; and the balance water. The preparation method comprises the following steps: injecting water into a batching tank, starting a stirrer, sequentially adding aluminum sulfate, calcium sulfide and bentonite, and stirring at room temperature, so that the bentonite is fully hydrated and dispersed, and the aluminum sulfate and calcium sulfide powder is uniformly dispersed in the water. The high-temperature plugging control plugging agent for the steam injection well is an inorganic cementing material, has relatively long gelation time, good construction safety, pumping performance, proper structural strength, relatively good high temperature resistance and other properties, has the properties required by high-temperature plugging control and channeling sealing materials, and has good adaptability in plugging control and channeling sealing of heavy oil thermal recovery and steam injection wells.

Description

Technical Field

[0001] The invention relates to a high-temperature profile control plugging agent for steam injection wells. Background Art

[0002] During the development of heavy oil reservoirs, long-term mining activities lead to the withdrawal of large amounts of crude oil from the formation, resulting in a gradual depletion of the formation. This leads to a gradual increase in the water content of the oil wells, and the formation of high-water-cut zones in some areas. These high-water-cut zones not only reduce the oil well's crude oil yield but also increase production costs. High-temperature profile control plugging agents can seal these high-water-cut zones, forcing the fluid to flow to other oil-bearing intervals, thereby increasing the oil well's recovery rate.

[0003] Currently, high-temperature profile control plugging agents primarily include traditional clay granules and polyacrylamide polymer gels. Clay granules are well-suited for plugging gasoline and water injection wells in the early stages of oil production. They can block small, initially pore-sized crossflow channels. However, due to significant inherent limitations, they are extremely ineffective in severely depleted formations. This is because traditional clay granules cannot form a strong, monolithic plug within the formation. Because clay is not hydraulically hardening, it does not gel within the formation and does not form a monolithic structure. Consequently, it quickly disintegrates under the impact of injected steam, leaving no plug after the steam passes through, resulting in failure of high-temperature profile control. These traditional granules are effective in the early stages of oil well production when formation depletion is relatively small. They can achieve a certain level of plugging through bridging and accumulation. However, with today's severely depleted formations, achieving this plugging effect through bridging and accumulation is impossible because bridges cannot form in such large channels and spaces. While traditional polyacrylamide gels can form a monolithic seal, they quickly decompose under the high temperatures of steam injection, losing their profile control and plugging properties. Therefore, for such formations, a completely different profile control and plugging material must be used: one that can form a monolithic structure interconnected within the formation spaces and crossflow channels, possesses sufficient mechanical strength, and can withstand the high-temperature impact of steam injection. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a high-temperature profile control plugging agent for steam injection wells, which has a long gel time, good construction safety, pumpability, appropriate structural strength and good resistance to high-temperature impact of steam injection, and has good adaptability in heavy oil thermal recovery and profile control and plugging of steam injection wells.

[0005] The technical solution of the present invention is: A high-temperature profile control and plugging agent for steam injection wells must be a material that can solidify and form structural strength in the formation; the profile control and plugging fluid of this material should have a certain stability, not obviously thicken on the ground and during pumping, and have good suspension stability to ensure the smooth progress and safety of pumping construction; after being injected into the formation, under the action of the formation temperature or the steam injection temperature, it can react and solidify after a certain period of time to form a profile control and plugging structure with a certain strength and capable of withstanding the high-temperature impact of steam injection.

[0006] The composition of the high-temperature plugging agent for steam injection wells is as follows according to the percentage by mass: Aluminum sulfate 5% to 10%; Calcium sulfide 10% to 15%; Bentonite 5% to 10%; Water balance.

[0007] Further preferably, the mass percentage of the aluminum sulfate is 7%.

[0008] Further preferably, the mass percentage of the calcium sulfide is 12%.

[0009] Further preferably, the mass percentage of the bentonite is 8%.

[0010] Further preferably, the specific preparation method of the high-temperature plugging agent for steam injection wells is: inject water into the batching tank, start the mixer, and then add aluminum sulfate, calcium sulfide and bentonite in sequence, and stir at room temperature to fully hydrate and disperse the bentonite and make the aluminum sulfate and calcium sulfide powders evenly dispersed in the water.

[0011] More preferably, the stirring time is 60 min.

[0012] The above-mentioned high-temperature plugging and sealing agent for steam injection wells is used in heavy oil thermal recovery and plugging and sealing of steam injection wells.

[0013] Furthermore, when in use, the high-temperature plugging agent of the steam injection well in the wellbore is pushed into the formation with clean water, and then steam injection production is carried out.

[0014] This application develops a high-temperature steam injection well plugging material with aluminum sulfate and calcium sulfide as its main components, capable of solidifying in the formation. Aluminum sulfate, under the alkaline conditions of a calcium sulfide solution, at the formation temperature and steam injection temperature, transforms into amorphous hydrous aluminum oxide with pozzolanic activity. Calcium sulfide, under the influence of formation temperature, particularly steam injection temperature, hydrolyzes into alkaline calcium hydroxide (slaked lime). These amorphous hydrous aluminum oxides react with calcium hydroxide under the influence of the high temperature of steam injection, producing calcium aluminate and calcium sulfoaluminate crystals that solidify and harden, achieving formation profile control and channeling prevention.

[0015] The present application also uses bentonite as a suspending agent to suspend the calcium sulfide powder and the generated amorphous hydrous aluminum oxide, so as to facilitate the largest possible sealing volume after injection and hardening.

[0016] The calcium sulfide in this application can hydrolyze in water to form slaked lime (Ca(OH)2). Aluminum sulfate can hydrolyze in an alkaline solution containing slaked lime to form Al(OH)3 and CaSO4. Here, Al(OH)3 is an amorphous gel precipitate, actually amorphous hydrous aluminum oxide (Al2O3.xH2O) with variable water content, which exhibits high pozzolanic reactivity. Under high-temperature steam injection conditions, the slaked lime produced by the hydrolysis of CaS can react with the amorphous Al2O3.xH2O produced by the Al2(SO4)3 to form calcium aluminate crystals such as monocalcium aluminate (CaO.Al2O3), monocalcium dialuminate (CaO.2Al2O3), and dodecaluminate (12CaO.7Al2O3). Furthermore, the CaSO4 produced by the hydrolysis of CaS can react with Ca(OH)2 and Al2O3.xH2O to form calcium sulfoaluminate (3CaO.3Al2O3.CaSO4) crystals. These calcium aluminate crystals can all produce structural strength, among which CaO.Al2O3 and CaO.2Al2O3 have higher strength. In 12CaO.7Al2O3 crystals, due to the extremely irregular coordination of aluminum and calcium, there are a large number of pores in the structure, and the water content is high. The strength is not as high as CaO.Al2O3 and CaO.2Al2O3, but because the formed structure has a larger volume, it is very suitable for profile control and plugging applications. Therefore, by controlling the ratio between CaS and Al2(SO4)3, the relative proportions of Ca(OH)2 and Al2O3.xH2O can be adjusted, and the composition ratios of the various crystals of 12CaO.7Al2O3, CaO.2Al2O3, and CaO.Al2O3 in the profile control and plugging solid can be controlled. The formula of this application is designed to produce a profile control and plugging solid with 12CaO.7Al2O3 as the main component and CaO.Al2O3 as the auxiliary component, and very few CaO.2Al2O3 and 3CaO.3Al2O3.CaSO4 crystals. This type of profile control and plugging solidified material has more pores in its structure. Although its strength is slightly lower, this strength is sufficient to meet the profile control and plugging requirements. Moreover, the same concentration of high-temperature profile control and plugging agent for steam injection wells can form a larger volume of solidified plugging material, with high profile control and plugging efficiency.

[0017] The rate of the above-mentioned volcanic ash reaction between amorphous hydrous aluminum oxide and calcium hydroxide depends on the decomposition rate of aluminum sulfate and calcium sulfide, as well as the reaction rate of the volcanic ash reaction between the two. Under normal circumstances, the rate at which aluminum sulfate generates amorphous hydrous aluminum oxide is relatively fast, and the rate at which calcium sulfide decomposes into slaked lime is relatively slow. Increasing the temperature can accelerate the decomposition of calcium sulfide. Under ground temperature conditions, the volcanic ash reaction between amorphous hydrous aluminum oxide and slaked lime is very slow, but it can proceed rapidly above 200°C and can form sufficient plugging strength. Therefore, the high-temperature plugging agent for steam injection wells of the present application has the properties of a plugging material that "does not thicken and harden on the ground and during injection" and "can gradually harden after entering the formation", that is, it has the basic conditions for being used as a high-temperature plugging material.

[0018] The present application uses bentonite as a suspending agent and dispersing agent for calcium sulfide and amorphous hydrous aluminum oxide, so that calcium sulfide and amorphous hydrous aluminum oxide are stably suspended and evenly dispersed in the high-temperature plugging agent for steam injection wells. The bentonite of the present application uses calcium-based bentonite. When there is a sufficient amount of Ca in the high-temperature plugging agent for steam injection wells, the calcium sulfide and amorphous hydrous aluminum oxide are stably suspended and evenly dispersed in the high-temperature plugging agent for steam injection wells. 2+ Mg 2+ When high-valent cations are present, the bentonite will undergo a "high-temperature curing reaction" under high-temperature steam injection conditions. 2+ Mg 2+ The cations combine with the Si-O and Al-O bonds around the bentonite flaky particles to form crystals such as hydrated calcium silicate or hydrated magnesium aluminate, which "weld" the montmorillonite flaky particles together to form a rigid structure and solidify. This high-temperature solidification reaction of bentonite is similar to the volcanic ash reaction of materials containing active silica, active alumina, etc. with calcium hydroxide to form hydrated calcium silicate, hydrated calcium aluminate or hydrated calcium sulfoaluminate. That is, the bentonite in this application can also form a certain structural strength under high temperature conditions and also has a high-temperature plugging effect. Sufficient Ca 2+ The ions are provided by calcium sulfide.

[0019] The beneficial effects of the present invention are: (1) Good safety and pumpability. The viscosity of the high-temperature plugging agent for steam injection wells is low, about 10mPa.s at 45°C, and can be maintained for 2-3 days without significant changes. During this period, the slurry basically has no water seepage. That is to say, under normal temperature and pressure conditions, the high-temperature plugging fluid for steam injection wells will not undergo hydration reaction on its own, so it will not significantly thicken on its own, let alone gel solidification. Its viscosity can be stable for a long time, so it has very high safety. During the injection process, there is no need to worry about accidents such as cementing operations. At the same time, the low viscosity also ensures the good injection performance of the high-temperature plugging agent for steam injection wells, and conventional injection equipment such as profile control pumps and cement trucks can be used for injection construction.

[0020] (2) Outstanding high temperature resistance. The 12CaO·7Al2O3, CaO·Al2O3, CaO·2Al2O3, 3CaO·3Al2O3, and CaSO4 crystals formed after the high temperature profile control plugging agent for steam injection wells solidifies will not undergo crystal transformation at high temperatures. Therefore, they have outstanding high temperature resistance and are very suitable for profile control and channeling prevention in high temperature steam injection wells or thermal recovery wells.

[0021] (3) The compressive strength of the high-temperature plugging agent for steam injection wells after curing is not less than 1.0 MPa. This strength is sufficient to meet the requirements of profile control and sealing of formation crossflow channels, and can ensure that an overall plugging structure with sufficient strength is formed at the formation crossflow where profile control and sealing are required, and has a long profile control and sealing life under steam injection conditions.

[0022] (4) The high-temperature plugging and sealing agent for steam injection wells of the present invention is an inorganic gelling material. Although it does not have the strength of cement, it has the properties that high-temperature plugging and sealing materials should have, such as a long gel time, good construction safety, pumpability, appropriate structural strength and good high-temperature resistance. It has good adaptability in heavy oil thermal recovery and plugging and sealing of steam injection wells. DETAILED DESCRIPTION

[0023] The characteristics of the present invention will be further described below with reference to the embodiments.

[0024] The gel time of the high-temperature plugging agent for steam injection wells is determined by the loss of fluidity of the high-temperature plugging agent for steam injection wells in a high-pressure sealed tank; the strength of the gel solidification is measured using a universal strength testing machine.

[0025] Example 1 Considering the injection safety of high-temperature plugging agent for steam injection wells, the viscosity change of high-temperature plugging agent for steam injection wells at 45℃ was investigated.

[0026] The raw materials were weighed according to their mass percentages: 7% aluminum sulfate, 12% calcium sulfide, 8% bentonite and 73% tap water, and stirred at room temperature for 60 minutes to obtain a high-temperature plugging agent for steam injection wells.

[0027] The high-temperature plugging agent for steam injection wells prepared in Example 1 was kept at a constant temperature in a water bath at 45° C., and the viscosity change of the high-temperature plugging agent for steam injection wells at different times was measured. The experimental results are shown in Table 1.

[0028] Table 1 Stability of high temperature plugging agent for low temperature steam injection wells Time / h 1 24 48 72 96 Viscosity / mPa.s 10.1 10.4 10.5 10.7 10.7 The test results in Table 1 show that at 45°C, the high-temperature plugging agent for steam injection wells does not undergo hydration reaction to thicken and gel, and can remain stable for a relatively long time. This shows that the high-temperature plugging agent for steam injection wells is sufficiently stable under ground temperature conditions and can fully meet the plugging injection time requirements.

[0029] The high-temperature plugging agent for steam injection wells prepared in Example 1 was placed in a sealed tank and heated at constant temperatures of 150°C, 200°C, 250°C, and 300°C for 24 hours, and the compressive strengths were 0.3 MPa, 1.8 MPa, 2.3 MPa, and 2.7 MPa, respectively.

[0030] Example 2 The raw materials were weighed according to their mass percentages: 5% aluminum sulfate, 10% calcium sulfide, 5% bentonite and 80% tap water, and stirred at room temperature (25° C.) for 60 minutes to obtain a high-temperature plugging agent for steam injection wells.

[0031] The high-temperature plugging agent for steam injection wells prepared in Example 2 was placed in a sealed tank and heated at constant temperatures of 150°C, 200°C, 250°C, and 300°C for 24 hours, and the compressive strengths were 0.1 MPa, 1.1 MPa, 1.3 MPa, and 1.6 MPa, respectively.

[0032] Example 3 The raw materials were weighed according to their mass percentages: 10% aluminum sulfate, 15% calcium sulfide, 10% bentonite and 65% tap water, and stirred at room temperature (25° C.) for 60 minutes to obtain a high-temperature plugging agent for steam injection wells.

[0033] The high-temperature plugging agent for steam injection wells prepared in Example 3 was placed in a sealed tank and heated at constant temperatures of 150°C, 200°C, 250°C, and 300°C for 24 hours, and the compressive strengths were 0.3 MPa, 2.1 MPa, 2.4 MPa, and 2.6 MPa, respectively.

[0034] From the compressive strength test results of Examples 1 to 3, it can be seen that the plugging strength formed at a temperature of 150°C is relatively low, and the plugging strength at a temperature of 200°C and above can fully meet the profile control and plugging requirements of steam injection wells.

[0035] The feeding ratio of the high-temperature plugging agent for steam injection wells of the present invention can be determined according to the degree of formation channeling. The formulation principle is roughly as follows: if the formation channeling pores are relatively small, the proportions of aluminum sulfate, calcium sulfide and bentonite in the plugging fluid are appropriately lower; if the channeling pores are large and numerous, the proportions of aluminum sulfate, calcium sulfide and bentonite are appropriately higher; if the injection volume is large, the concentration of the front slug should be lower, while the concentration of the rear slug should be appropriately higher; if the plugging strength requirement is high, the proportions of aluminum sulfate, calcium sulfide and bentonite in the plugging fluid are appropriately higher; if the plugging strength requirement is low, the concentrations of aluminum sulfate, calcium sulfide and bentonite can be appropriately lower.

[0036] The water used to prepare the high-temperature plugging agent for steam injection wells can be injection water, tap water or oilfield produced water, and the water temperature is less than 45°C. The preparation procedures of the high-temperature plugging agent for steam injection wells in Examples 1 to 3 of the present invention are as follows: (1) Take the formulated amount of aluminum sulfate, calcium sulfide, bentonite and dosing water according to the volume of the dosing tank; (2) Start the mixer and add materials in the order of water → aluminum sulfate → calcium sulfide → bentonite, so that the bentonite is fully hydrated and dispersed and the calcium sulfide and aluminum sulfate powders are evenly dispersed in the water, and continue stirring to form a uniform and stable high-temperature plugging agent for steam injection wells; (3) Injecting high-temperature plugging agent into the steam injection well into the formation; (4) Use clean water to push the profile control and plugging fluid in the wellbore into the formation; (5) Steam injection production.

[0037] A general approach is to use a general injection process, utilizing the injection and production tubing within the well to inject high-temperature plugging agents for steam injection wells. This process is simple to implement and requires no tubing changes. This injection method exploits the heterogeneous permeability of the formation. During injection, the working fluid primarily enters high-permeability layers, as these have low flow resistance. High-permeability layers are often high-water-bearing, precisely the areas requiring plugging and channeling control. Therefore, the varying permeabilities of the formations can be exploited to achieve the selective injection of high-temperature plugging agents for steam injection wells.

[0038] The above are only specific embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A high-temperature plugging agent for steam injection wells, characterized by: The composition according to mass percentage is as follows: Aluminum sulfate 5% to 10%; Calcium sulfide 10% to 15%; Bentonite 5% to 10%; Water balance.

2. The high-temperature plugging agent for steam injection wells according to claim 1, characterized in that: The mass percentage of the aluminum sulfate is 7%.

3. The high-temperature plugging agent for steam injection wells according to claim 1, characterized in that: The mass percentage of the calcium sulfide is 12%.

4. The high-temperature plugging agent for steam injection wells according to claim 1, characterized in that: The mass percentage of the bentonite is 8%.

5. The high-temperature plugging agent for steam injection wells according to claim 1, characterized in that: The specific preparation method is: inject water into the batching tank, turn on the mixer, and then add aluminum sulfate, calcium sulfide and bentonite in sequence, stir at room temperature, so that the bentonite is fully hydrated and dispersed, and the aluminum sulfate and calcium sulfide powders are evenly dispersed in the water.

6. The high-temperature plugging agent for steam injection wells according to claim 5, characterized in that: When stirring, the stirring time is 60 minutes.

7. Use of the high-temperature plugging and sealing agent for steam injection wells according to claim 1 in heavy oil thermal recovery and plugging and sealing of steam injection wells.