Plugging agent and preparation method thereof

Abstract

The invention discloses a plugging agent and a preparation method thereof, the plugging agent comprises bentonite, cement and a retarder, the mass ratio of the bentonite to the cement is 1: 15, and the water-cement ratio of the cement is 5-7; the retarder is a hydroxyl-containing cellulose polymer and citric acid, the ratio of the hydroxyl-containing cellulose polymer to the water is (1: 1000)-(1: 1500), and the addition amount of the citric acid is 0.1-0.3% of the total mass of the bentonite, the cement and the retarder; the plugging agent provided by the invention can effectively prolong the initial setting time, and provides objective conditions for the plugging agent to enter a deeper layer to play a role in plugging formation water outlet ducts, so that the problems of short initial setting time and small plugging radius of an existing plugging agent are fundamentally solved.

Description

Technical Field

[0001] The present disclosure relates to the technical field of oilfield chemistry, and in particular to a plugging agent for advantageous seepage channels after water flooding and chemical flooding in oilfields. Background Art

[0002] The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

[0003] The development of deep injection well profile control technology can be roughly divided into two phases. The first phase is near-wellbore profile control, which primarily addresses heterogeneity between reservoirs. This typically employs strong gels, but this approach has a relatively small operating radius. The second phase is deep reservoir profile control, which is primarily used in the final stages of oilfield development because the residual oil volume in the injection well zone is small and subject to turbulent flow, resulting in suboptimal overall oil production from injection well profile control. This profile control primarily involves injecting mobile gels or particles into larger fractures or pores within the formation to improve sweep efficiency.

[0004] Typically, oilfields that require profile control require high-dose, multi-stage plugging treatments, requiring large amounts of profile control and water plugging agents. Currently, most oilfields use plugging agents based on inorganic cement, which has a short initial setting time and a small plugging radius.

[0005] It should be noted that the information disclosed in the above background technology section is only used to enhance the understanding of the background of the present disclosure, and therefore may contain information that does not constitute prior art. Summary of the Invention

[0006] In view of this, the present disclosure provides a plugging agent and a preparation method thereof, which solve the problems of short initial setting time and small plugging radius of existing plugging agents.

[0007] To achieve the above-mentioned purpose of the invention, in a first aspect, the plugging agent comprises:

[0008] Bentonite, cement and retarder, wherein the mass ratio of the bentonite to the cement is 1:15, and the water-cement ratio of the cement is 5-7;

[0009] The retarder is a hydroxyl-containing cellulose polymer and citric acid. The ratio of the hydroxyl-containing cellulose polymer to water is 1:1000 to 1:1500. The amount of citric acid added is 0.1% to 0.3% of the total mass of the bentonite, cement and retarder.

[0010] In the present disclosure and possible embodiments, the hydroxyl-containing cellulose polymer is sodium carboxymethyl cellulose.

[0011] In the present disclosure and possible embodiments, the components further include a reinforcing agent.

[0012] In the present disclosure and possible embodiments, the reinforcing agent is phosphogypsum.

[0013] In the present disclosure and possible embodiments, the amount of the phosphogypsum is 0.1% to 0.2% of the total mass of the bentonite, cement and retarder.

[0014] In the present disclosure and possible embodiments, the cement has a particle size of 200 mesh.

[0015] In the present disclosure and possible embodiments, the bentonite has a particle size of 200 mesh.

[0016] In a second aspect, a method for preparing the plugging agent according to the first aspect comprises:

[0017] A hydroxyl-containing cellulose polymer is prepared into a polymer mother liquor, cement, bentonite, citric acid, a reinforcing agent and water are added to the polymer mother liquor while stirring, and the mixture is stirred evenly to obtain the plugging agent.

[0018] In the present disclosure and possible embodiments, the method of preparing a polymer mother solution includes:

[0019] The hydroxyl-containing cellulose polymer is mixed with water in a set ratio, and aged in a maturation tank for more than 2 hours to obtain the polymer mother solution.

[0020] The present disclosure has the following beneficial effects:

[0021] The plugging agent disclosed herein enhances the water retention of the profile control and water plugging agent by adding a retarder, thereby enhancing the fluidity of the slurry and promoting more slurry to enter the formation, thereby greatly increasing the initial setting time of the profile control system, and providing objective conditions for the plugging agent to enter deeper layers to play a role in plugging the water outlet channels of the formation; in addition, the addition of the reinforcing agent improves the solidification strength of the profile control and water plugging agent slurry after entering the formation, and the specific compressive strength can reach 20 MPa; therefore, the plugging agent of the present invention is fully capable of performing the task of profile control in the deep and middle parts of the advantageous seepage channels, and effectively solves the problems of short initial setting time and small plugging radius of existing plugging agents. DETAILED DESCRIPTION

[0022] The present disclosure is described below based on embodiments, but it is worth noting that the present disclosure is not limited to these embodiments. In the detailed description of the present disclosure below, some specific details are described in detail. However, for the parts not described in detail, those skilled in the art can also fully understand the present disclosure.

[0023] At the same time, unless the context clearly requires otherwise, words such as "include", "comprising" and the like throughout the specification and claims should be interpreted as inclusive rather than exclusive or exhaustive; that is, as "including but not limited to".

[0024] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, specific embodiments are listed below to further illustrate the present invention in detail.

[0025] In each embodiment of the present disclosure, the preparation method of the plugging agent is as follows:

[0026] 1. Preparation of polymer masterbatch

[0027] The hydroxyl-containing cellulose polymer dry powder is mixed with water and aged in a maturation tank for more than 2 hours to prepare a polymer mother liquor for standby use.

[0028] 2. Preparation of plugging agent

[0029] According to the design plan, cement, bentonite, citric acid, reinforcing agent and water are added to the prepared polymer mother liquor while stirring, and the plugging agent is obtained after uniform stirring.

[0030] 3. Plugging agent injection

[0031] The prepared plugging agent is kept in a stirring state and injected into a single well through an injection pump.

[0032] Example 1

[0033] Raw material ratio: see Table 1 below.

[0034] Preparation of the plugging agent: Sodium carboxymethyl cellulose was mixed with water and matured in a maturation tank for 3 hours to prepare a polymer mother liquor; cement, bentonite, citric acid, phosphogypsum and water were added to the prepared polymer mother liquor while stirring, and the plugging agent of Example 1 was obtained after uniform stirring.

[0035] After testing, the initial setting time, final setting time and compressive strength of the plugging agent of Example 1 are shown in Table 1 below:

[0036] Table 1 Raw material ratio, initial setting and final setting time, compressive strength (wet mix)

[0037]

[0038]

[0039] Table 1 shows that the initial setting time can be controlled by controlling the content of various components, such as polymer concentration, water-cement ratio, citric acid concentration, and phosphogypsum concentration. Increasing the polymer concentration, water-cement ratio, and citric acid concentration, while decreasing the phosphogypsum concentration, can extend the initial setting time. The initial setting time can reach 260 hours, and the compressive strength can reach 20 MPa. Therefore, the plugging agent is fully capable of controlling the profile of deep and mid-range areas in dominant seepage channels.

[0040] Retarder and enhancer are contradictory. Increasing the amount of citric acid will extend the initial setting time, but will reduce the compressive strength. Increasing the amount of enhancer will increase the compressive strength of the plugging agent, but will inhibit the initial setting time. When only retarder is added, the initial setting time of the plugging agent can reach 120h, while after adding enhancer, the initial setting time is around 80h, but the compressive strength is stable at 22MPa. Therefore, if too much retarder is added, the compressive strength of the plugging agent will be affected, and if too much enhancer is added, the initial setting time of the plugging agent will be affected. Mixing retarder and enhancer in a certain proportion can achieve compressive strength and initial setting time that meet process requirements and technical indicators.

[0041] Example 2

[0042] The raw material ratio is: the mass ratio of sodium carboxymethyl cellulose to water is 1:1500, the water-cement ratio is 7, the ratio of bentonite to cement is 1:15, citric acid is 0.1% of the total mass, and phosphogypsum is 0.1% of the total mass.

[0043] Preparation of plugging agent: The plugging agent of Example 2 was prepared in the same manner as in Example 1. Testing showed that the initial setting time of the plugging agent of Example 2 was 40 hours, which was just appropriate for plugging near the wellbore.

[0044] If the raw material ratio is changed to: the ratio of sodium carboxymethyl cellulose to water is 1:1500, the water-cement ratio is 7, the ratio of bentonite to cement is 1:15, citric acid is 0.2% of the total mass, and phosphogypsum is 0.1% of the total mass, the mixture is evenly stirred.

[0045] The test results show that the initial setting time is 87h, which is relatively long, with strong stability and slow sedimentation rate, making it suitable for on-site application.

[0046] If the raw material ratio is changed to: the ratio of sodium carboxymethyl cellulose to water is 1:1500, the water-cement ratio is 7, the ratio of bentonite to cement is 1:15, citric acid is 0.3% of the total mass, and phosphogypsum is 0.1% of the total mass, the mixture is evenly stirred.

[0047] The test results show that the initial setting time is 106h, which is relatively long, with strong stability and slow sedimentation rate, making it suitable for deep reservoir plugging.

[0048] The indoor experiment of Example 2 proves that, under the condition of constant contents of other components in the plugging system, the initial setting time is prolonged with the increase of citric acid.

[0049] Example 3

[0050] The raw material ratio is: water-cement ratio is 7, the ratio of bentonite to cement is 1:15, citric acid is 0.3% of the total mass, phosphogypsum is 0.1% of the total mass, and the ratio of sodium carboxymethyl cellulose to water is 1:1500.

[0051] Preparation of plugging agent: The same as Example 1 was used to obtain the plugging agent of Example 3.

[0052] According to the test, the initial setting time of the plugging agent in Example 3 is 106 hours.

[0053] If the raw material ratio is changed to: the ratio of sodium carboxymethyl cellulose to water is 1:1000, the water-cement ratio is 7, the ratio of bentonite to cement is 1:15, citric acid is 0.3% of the total mass, and phosphogypsum is 0.1% of the total mass.

[0054] The test results show that the initial setting time is 134h, which is relatively long, with strong stability and slow sedimentation rate, making it suitable for on-site application.

[0055] If the raw material ratio is changed to: the ratio of sodium carboxymethyl cellulose to water is 1:500, the water-cement ratio is 7, the ratio of bentonite to cement is 1:15, citric acid is 0.3% of the total mass, and phosphogypsum is 0.1% of the total mass.

[0056] The test results show that the initial setting time is 192h, which means the initial setting time is long, the stability is strong, and the sedimentation rate is slow, which is suitable for on-site application.

[0057] The indoor experiment of Example 3 proves that, under the condition of constant contents of other components in the plugging system, the initial setting time is prolonged with the increase of sodium carboxymethyl cellulose.

[0058] Example 4

[0059] The raw material ratio is: the ratio of bentonite to cement is 1:15, citric acid is 0.3% of the total mass, phosphogypsum is 0.1% of the total mass, the ratio of sodium carboxymethyl cellulose to water is 1:1000, and the water-cement ratio is 7.

[0060] Preparation of plugging agent: The same as Example 1 was used to obtain the plugging agent of Example 4.

[0061] According to the test, the initial setting time of the plugging agent in Example 4 is 134 hours.

[0062] If the raw material ratio is changed to: the ratio of bentonite to cement is 1:15, citric acid is 0.3% of the total mass, phosphogypsum is 0.1% of the total mass, the ratio of sodium carboxymethyl cellulose to water is 1:1000, and the water-cement ratio is 5.

[0063] The test results show that the initial setting time is 80h, and the initial setting time is shortened.

[0064] The indoor experiment of Example 4 proves that, under the condition of constant contents of other components in the plugging system, the initial setting time is prolonged with the increase of the water-cement ratio.

[0065] Example 5

[0066] The raw material ratio is: water-cement ratio is 7, the ratio of bentonite to cement is 1:15, citric acid is 0.3% of the total mass, phosphogypsum is 0.1% of the total mass, and the ratio of sodium carboxymethyl cellulose to water is 1:1000.

[0067] Preparation of plugging agent: The same as Example 1 was used to obtain the plugging agent of Example 5.

[0068] According to the test, the initial setting time of the plugging agent in Example 5 is 134 hours.

[0069] If the ratio of raw materials remains unchanged: the ratio of bentonite to cement is 1:15, citric acid is 0.3% of the total mass, phosphogypsum is 0.1% of the total mass, the cement dosage is 7 with a water-cement ratio, and the ratio of sodium carboxymethyl cellulose to water is 1:1000.

[0070] The test result shows that the initial setting time is 146h, which is not much different from the initial setting time of wet mix.

[0071] The comparison between wet mixing and dry mixing in Example 5 is shown in Table 2:

[0072] Table 2 Comparison of wet mixing and dry mixing

[0073]

[0074]

[0075] The indoor experiments of Example 5 show that the dry mixing forms a plugging system with an initial setting time that is not much different from that of the wet mixing, which can significantly reduce the workload during on-site construction and eliminate the preparation and maturation process of the polymer solution.

[0076] It can be seen from the above examples that the plugging agent disclosed in the present invention can effectively increase the plugging radius and prolong the initial setting time for deep plugging in advantageous permeability channels. Most granular profile control agents on the market have high viscosity and short initial setting time, making it difficult to enter deep oil wells, and require the addition of multiple chemical agents, which is troublesome to operate and is not conducive to practical application on site. The present invention solves these problems and truly enters on-site construction applications, with broad application prospects in the process of oil and gas development. The sodium carboxymethyl cellulose in the present invention is pre-mixed and injected in advance, which greatly reduces the difficulty of on-site application and storage, and the initial setting time of the formula is the shortest at 36h and the longest at 260h. The average initial setting time reaches more than 60h, which is much longer than the initial setting time of the plugging agents on the market. The retarder can greatly increase the initial setting time of the profile control system, providing objective conditions for the plugging agent to enter deeper layers to play a plugging role in the water outlet pores of the formation.

[0077] Moreover, the plugging agent disclosed in the present invention uses inorganic ordinary cement as the main agent of the profile control agent, bentonite as the auxiliary agent, sodium carboxymethyl cellulose and citric acid as retarders, and phosphogypsum as the reinforcing agent. While reducing the viscosity, it ensures that the initial setting time is controllable and long, the plugging radius is large, and permanent plugging can be achieved.

[0078] Furthermore, the main component of the profile control agent is an inorganic substance with strong aging resistance and a long plugging period. The auxiliary components of the profile control agent are few and the dosage is small, effectively reducing the production cost of on-site preparation of the plugging agent. The bentonite particle size selected for plugging in mid-depth areas reaches 200 mesh, making the entire slurry particle size smaller, thereby further plugging the pores in deeper formations. Furthermore, the selected phosphogypsum as a reinforcing agent has the advantages of being readily available and economical. Furthermore, the addition of sodium carboxymethyl cellulose allows for both dry and wet mixing on-site in the oilfield, effectively reducing the complexity of on-site mixing operations.

[0079] Therefore, the plugging agent disclosed in the present invention meets the requirements of on-site economy and ease of operation, and has high practicality.

[0080] The above-described embodiments are merely examples of implementation methods of the present disclosure, and their descriptions are relatively specific and detailed. However, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art may make various modifications, equivalent substitutions, and improvements without departing from the scope of the present disclosure, and these modifications are all within the scope of protection of the present disclosure. Therefore, the scope of protection of the present invention shall be based on the appended claims.

Claims

1. A plugging agent, characterized in that: Its components include: Bentonite, cement and retarder, wherein the mass ratio of the bentonite to the cement is 1:15, and the water-cement ratio of the cement is 5-7; The retarder is a hydroxyl-containing cellulose polymer and citric acid. The ratio of the hydroxyl-containing cellulose polymer to water is 1:1000 to 1:1500. The amount of citric acid added is 0.1% to 0.3% of the total mass of the bentonite, cement and retarder.

2. The plugging agent according to claim 1, characterized in that: The hydroxyl-containing cellulose polymer is sodium carboxymethyl cellulose.

3. The plugging agent according to claim 1 or 2, characterized in that: The composition also includes a reinforcing agent.

4. The plugging agent according to claim 3, characterized in that: The reinforcing agent is phosphogypsum.

5. The plugging agent according to claim 4, characterized in that: The amount of the phosphogypsum is 0.1% to 0.2% of the total mass of the bentonite, cement and retarder.

6. The plugging agent according to claim 1, 2, 4 or 5, characterized in that: The particle size of the cement is 200 mesh.

7. The plugging agent according to claim 6, characterized in that: The particle size of the bentonite is 200 mesh.

8. The method for preparing the plugging agent according to any one of claims 1 to 7, characterized in that: include: A hydroxyl-containing cellulose polymer is prepared into a polymer mother liquor, cement, bentonite, citric acid, a reinforcing agent and water are added to the polymer mother liquor while stirring, and the mixture is stirred evenly to obtain the plugging agent.

9. The method for preparing the plugging agent according to claim 8, characterized in that: The method for configuring a polymer mother solution comprises: The hydroxyl-containing cellulose polymer is mixed with water in a set ratio, and aged in a maturation tank for more than 2 hours to obtain the polymer mother solution.

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