阅读说明：本技术 一种淀粉改性物、淀粉基压裂暂堵剂及其制备方法和使用方法 (Starch modifier, starch-based fracturing temporary plugging agent, and preparation method and use method thereof ) 是由 廖乐军 韩文哲 白茹 陈亚联 刘小会 周建柱 李楠 关宏生 白田民 王晨 秋列维 于 2021-07-05 设计创作，主要内容包括：本发明提供了一种淀粉改性物、淀粉基压裂暂堵剂及其制备方法和使用方法,淀粉改性物通过烷基烯酮二聚体与淀粉中的羟基在中碱性条件下反应得到。淀粉基压裂暂堵剂包括硬脂酸钙和淀粉改性物,硬脂酸钙占淀粉改性物悬浮液和硬脂酸钙的总质量的质量百分比为5-10%。该淀粉基压裂暂堵剂作为一种新型的暂堵剂应用于油田开采中,该暂堵剂的合成不需要经过复杂的人工聚合,只需在一定温度下进行共混反应即可,充分利用淀粉分子聚合物结构所具有的强度对于裂缝进行堵塞,同时掺杂硬脂酸钙粒子,进一步提高物理强度,AKD的引入,降低了淀粉分子表面的亲水性,减缓了水分对淀粉晶区和非晶区的侵入和降解作用,减缓了其解堵时间。(The invention provides a starch modifier, a starch-based fracturing temporary plugging agent, a preparation method and a use method thereof. The starch-based fracturing temporary plugging agent comprises calcium stearate and a starch modifier, wherein the mass percentage of the calcium stearate in the total mass of the starch modifier suspension and the calcium stearate is 5-10%. This starch-based fracturing temporary plugging agent is applied to the oil field exploitation as neotype temporary plugging agent, the synthesis of this temporary plugging agent need not pass through complicated artifical polymerization, only need carry out blending reaction under the uniform temperature can, the intensity that make full use of starch molecule polymer structure has blocks up to the crack, mix calcium stearate particle simultaneously, further improve physical strength, AKD's introduction, the hydrophilicity on starch molecule surface has been reduced, the invasion and the degradation effect of moisture to starch crystalline region and amorphous region have been slowed down, its unblock time has been slowed down.)

1. A starch modifier characterized by: under the condition of medium alkalinity, the alkyl ketene dimer reacts with hydroxyl in starch to obtain the compound with the following structural formula:

wherein R is C₁₂~C₁₈Long-chain alkanes of (a); and n is the degree of polymerization.

2. A starch modifier according to claim 1, wherein: the starch is amylopectin or amylose, the polymerization degree n of the amylose is 300-40000, and the polymerization degree n of the amylopectin is 4000-40000.

3. The method for preparing a starch modifier according to claim 1, wherein: adding starch and alkyl ketene dimer into a solvent, stirring at 50-60 ℃, and fully reacting for 1-3h to obtain a starch modified substance suspension; wherein, the mass percentages of the starch and the alkyl ketene dimer are respectively 10-20% and 5-8%, and the balance is solvent.

4. The method for preparing a starch modifier according to claim 3, wherein: the solvent is toluene or acetone, and when the solvent is acetone, a reflux condensing device is required to be added.

5. A starch-based fracturing temporary plugging agent is characterized in that: the modified starch comprises calcium stearate and the modified starch as claimed in any one of claims 1 to 2, wherein the mass percentage of the calcium stearate to the total mass of the modified starch suspension and the calcium stearate is 5 to 10 percent, and the modified starch suspension is a mixed solution of the modified starch and a solvent.

6. The starch-based fracture temporary plugging agent according to claim 5, wherein: the solvent is toluene or acetone.

7. The method of claim 5, wherein the starch-based fracture temporary plugging agent is prepared by the following steps: adding the calcium stearate with the formula amount into the starch modified suspension, fully stirring for 1-2h, centrifuging the obtained suspension, taking the precipitate, and drying to obtain the starch-based temporary fracturing plugging agent.

8. The method of using a starch-based fracture temporary plugging agent according to claim 5, wherein: when the starch-based fracturing temporary plugging agent is used for temporary plugging fracturing, the mass concentration of the starch-based fracturing temporary plugging agent is 4-6%.

Technical Field

The invention belongs to the technical field of temporary plugging agents, and particularly relates to a starch modifier, a starch-based fracturing temporary plugging agent, and a preparation method and a use method thereof.

Background

In the hydraulic fracturing operation, when fracturing fluid enters a reservoir, due to the influence of formation cracks, a propping agent can block pores, so that the oil production efficiency is reduced, and the like. The temporary plugging agent can effectively plug cracks of formation pores, damage of fracturing fluid to formation permeability is reduced, and after plugging is finished, a plugging layer is damaged by different action principles such as temperature, pressure and solubility, so that the permeability of the formation is recovered, and the aim of improving the transformation effect is fulfilled.

The conventional temporary plugging agent is a water-soluble temporary plugging agent, and the purpose of temporary plugging of cracks is achieved by increasing viscoelasticity of fracturing fluid and losing fluidity and water solubility. The starch graft copolymer temporary plugging agent has excellent biodegradability and environmental protection performance, is wide in application, wide in source and low in price, and belongs to renewable resources. The traditional starch fracturing temporary plugging agent is used for grafting a copolymer on the basis of gelatinized starch, so that the excellent performances of temperature resistance, salt resistance and the like are improved, and the starch fracturing temporary plugging agent is used as a tackifier and a temporary plugging agent for oil and gas field exploitation.

Disclosure of Invention

The invention aims to provide a starch modifier, which overcomes the technical problems of the existing starch graft copolymer.

The invention also aims to provide a starch-based fracturing temporary plugging agent, which utilizes the self viscosity and adsorbability of modified starch to adsorb the modified starch and calcium stearate, thereby improving the physical strength of the temporary plugging agent and having better temporary plugging effect.

The invention also aims to provide a preparation method of the starch-based fracturing temporary plugging agent, which is simple and feasible and does not need complicated artificial polymerization.

The invention also provides a use method of the starch-based fracturing temporary plugging agent, which can effectively plug a crack in oil field exploitation.

Therefore, the technical scheme provided by the invention is as follows:

a modified starch is prepared by reacting alkyl ketene dimer with hydroxyl in starch under medium-alkaline condition, and has the following structural formula:

wherein R is C₁₂~C₁₈Long-chain alkanes of (a); and n is the degree of polymerization.

The starch is amylopectin or amylose, the polymerization degree n of the amylose is 300-40000, and the polymerization degree n of the amylopectin is 4000-40000.

Adding starch and alkyl ketene dimer into a solvent, stirring at 50-60 ℃, and fully reacting for 1-3h to obtain a starch modifier suspension; wherein, the mass percentages of the starch and the alkyl ketene dimer are respectively 10-20% and 5-8%, and the balance is solvent.

The solvent is toluene or acetone, and when the solvent is acetone, a reflux condensing device is required to be added.

The starch-based temporary plugging agent for fracturing comprises calcium stearate and a starch modifier, wherein the calcium stearate accounts for 5-10% of the total mass of a starch modifier suspension and the calcium stearate, and the starch modifier suspension is a mixed solution of the starch modifier and a solvent.

The solvent is toluene or acetone.

A preparation method of a starch-based fracturing temporary plugging agent is characterized by comprising the following steps: adding the calcium stearate with the formula amount into the starch modified suspension, fully stirring for 1-2h, centrifuging the obtained suspension, taking the precipitate, and drying to obtain the starch-based temporary fracturing plugging agent.

A using method of a starch-based fracturing temporary plugging agent is used for temporarily plugging fracturing, wherein the mass concentration of the starch-based fracturing temporary plugging agent is 4-6%.

The invention has the beneficial effects that:

the starch modifier provided by the invention modifies starch through Alkyl Ketene Dimer (AKD), under the condition of medium alkalinity, the AKD reacts with hydroxyl in starch molecules, and is combined with the starch molecules in a covalent bond form, so that the surface of the starch molecules is changed from hydrophilic to hydrophobic, and the degradation rate of the starch molecules is reduced.

The starch-based fracturing temporary plugging agent can adsorb insoluble particles such as calcium stearate and the like by utilizing the viscosity and the adsorbability of a starch modifier, thereby further improving the physical strength and playing a good temporary plugging effect.

The starch-based fracturing temporary plugging agent is applied to oilfield exploitation as a novel temporary plugging agent, the temporary plugging agent is synthesized without complex artificial polymerization and only needs to be subjected to blending reaction at a certain temperature, the temporary plugging mechanism is that the strength of a starch molecular polymer structure is fully utilized to block a crack, and calcium stearate particles are doped, so that the physical strength is further improved, the introduction of AKD (alkyl ketene dimer) reduces the hydrophilicity of the surface of a starch molecule, the invasion and degradation effects of moisture on a starch crystalline region and an amorphous region are slowed down, and the plugging removal time is slowed down.

As will be described in further detail below.

Drawings

FIG. 1 is a composite circuit diagram of the present invention.

Detailed Description

The following description of the embodiments of the present invention is provided for illustrative purposes, and other advantages and effects of the present invention will become apparent to those skilled in the art from the present disclosure.

The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein, which are provided for complete and complete disclosure of the present invention and to fully convey the scope of the invention to those skilled in the art. The terminology used in the description of the exemplary embodiments is not intended to be limiting of the invention.

Unless otherwise defined, terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Further, it will be understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense.

Example 1:

this example provides a starch modifier, which is obtained by reacting alkyl ketene dimer with hydroxyl group in starch under medium-alkaline condition, and has the following structural formula:

wherein R is C₁₂~C₁₈Long-chain alkanes of (a); and n is the degree of polymerization.

In the embodiment, Alkyl Ketene Dimer (AKD) reacts with hydroxyl in starch molecules and is combined with the starch molecules in a covalent bond mode, so that the surface of the starch molecules is changed from hydrophilic to hydrophobic, and the degradation rate of the starch molecules is reduced.

Example 2:

the embodiment provides a starch-based temporary plugging agent for fracturing, which comprises calcium stearate and a starch modifier, wherein the calcium stearate accounts for 5% of the total mass of a starch modifier suspension and the calcium stearate, and the starch modifier suspension is a mixed solution of the starch modifier and a solvent.

The preparation process comprises the following steps:

firstly, adding 10g of starch and 80g of toluene (solvent) into a three-neck flask, fully stirring for 2h at 20 ℃ to obtain a starch suspension, then heating to 50 ℃, slowly dropwise adding 5g of alkyl ketene dimer AKD by using a separating funnel, and after dropwise adding, continuously reacting for 2h at 50 ℃ to obtain a starch modified substance suspension.

And secondly, adding 5g of calcium stearate into the suspension of the starch modifier, fully stirring for 1h, centrifuging the obtained suspension, taking the precipitate, and drying to obtain the starch-based temporary plugging agent for fracturing.

In this example, the mass percentage of starch was 10%, the mass percentage of solvent was 80%, the mass percentage of alkyl ketene dimer was 5%, and the mass percentage of calcium stearate was 5%.

The principle of the invention is as follows:

according to the invention, starch is modified by AKD, and under the medium-alkaline condition, the AKD reacts with hydroxyl groups in starch molecules and is combined with the starch molecules in a covalent bond form, so that the surfaces of the starch molecules are changed from hydrophilic to hydrophobic, the degradation rate is reduced, and insoluble particles such as calcium stearate and the like can be adsorbed due to the viscosity and the adsorbability of the starch molecules, so that the physical strength is further improved, and a good temporary plugging effect is achieved.

The temporary plugging agent is synthesized without complex artificial polymerization, and only needs to be subjected to blending reaction at a certain temperature, as shown in figure 1. The temporary plugging mechanism is that the strength of a starch molecule polymer structure is fully utilized to plug cracks, calcium stearate particles are doped at the same time, the physical strength is further improved, the introduction of AKD reduces the hydrophilicity of the starch molecule surface, slows down the invasion and degradation of moisture to a starch crystal area and an amorphous area, and slows down the plugging removal time.

Example 3:

the embodiment provides a starch-based temporary plugging agent for fracturing, which comprises calcium stearate and a starch modifier, wherein the calcium stearate accounts for 8% of the total mass of a starch modifier suspension and the calcium stearate, and the starch modifier suspension is a mixed solution of the starch modifier and a solvent.

The preparation process comprises the following steps:

firstly, adding 15g of starch and 71g of toluene into a three-neck flask, fully stirring for 2h at 20 ℃ to obtain a starch suspension, then heating to 50 ℃, slowly dropwise adding 6g of AKD by using a separating funnel, and after the dropwise adding is finished, continuously reacting for 2h at 50 ℃ to obtain a starch modified substance suspension.

And secondly, adding 8g of calcium stearate into the suspension of the starch modifier, fully stirring for 1h, centrifuging the obtained suspension, taking the precipitate, and drying to obtain the starch-based temporary plugging agent for fracturing.

In this example, the mass percent of starch was 15%, the mass percent of solvent was 71%, the mass percent of alkyl ketene dimer was 6%, and the mass percent of calcium stearate was 8%.

Example 4:

the embodiment provides a starch-based temporary plugging agent for fracturing, which comprises calcium stearate and a starch modifier, wherein the calcium stearate accounts for 10% of the total mass of a starch modifier suspension and the calcium stearate, and the starch modifier suspension is a mixed solution of the starch modifier and a solvent.

The preparation process comprises the following steps:

step one, adding 20g of starch and 62g of toluene into a three-neck flask, fully stirring for 2 hours at 20 ℃ to obtain a starch suspension, then heating to 60 ℃, slowly dropwise adding 8g of AKD by using a separating funnel, and after the dropwise adding is finished, continuously reacting for 2 hours at 60 ℃ to obtain a starch modified substance suspension.

And secondly, adding 10g of calcium stearate into the suspension of the starch modifier, fully stirring for 1h, centrifuging the obtained suspension, taking the precipitate, and drying to obtain the starch-based temporary plugging agent for fracturing.

In this example, the mass percentage of starch was 20%, the mass percentage of solvent was 62%, the mass percentage of alkyl ketene dimer was 8%, and the mass percentage of calcium stearate was 10%.

Example 5:

the embodiment provides a starch-based temporary plugging agent for fracturing, which comprises calcium stearate and a starch modifier, wherein the calcium stearate accounts for 7% of the total mass of a starch modifier suspension and the calcium stearate, and the starch modifier suspension is a mixed solution of the starch modifier and a solvent.

The preparation process comprises the following steps:

firstly, adding 12g of starch and 76g of acetone (solvent) into a three-neck flask, fully stirring for 2h at 20 ℃ to obtain a starch suspension, then heating to 55 ℃, slowly dropwise adding 5g of AKD by using a separating funnel under reflux condensation, and after dropwise adding, continuously reacting for 2h at 55 ℃ to obtain a starch modified substance suspension.

And secondly, adding 7g of calcium stearate into the suspension of the starch modifier, fully stirring for 1h, centrifuging the obtained suspension, taking the precipitate, and drying to obtain the starch-based temporary plugging agent for fracturing.

In this example, the mass percent of starch was 12%, the mass percent of solvent was 76%, the mass percent of alkyl ketene dimer was 5%, and the mass percent of calcium stearate was 7%.

Example 6:

the embodiment provides a starch-based temporary plugging agent for fracturing, which comprises calcium stearate and a starch modifier, wherein the calcium stearate accounts for 10% of the total mass of a starch modifier suspension and the calcium stearate, and the starch modifier suspension is a mixed solution of the starch modifier and a solvent.

The preparation process comprises the following steps:

firstly, adding 18g of starch and 64g of acetone into a three-neck flask, fully stirring for 2 hours at 20 ℃ to obtain a starch suspension, then heating to 60 ℃, slowly dropwise adding 8g of AKD by using a separating funnel under reflux condensation, and after dropwise adding, continuously reacting for 2 hours at 60 ℃ to obtain a starch modified substance suspension.

And secondly, adding 10g of calcium stearate into the suspension of the starch modifier, fully stirring for 1h, centrifuging the obtained suspension, taking the precipitate, and drying to obtain the starch-based temporary plugging agent for fracturing.

In this example, the mass percent of starch was 18%, the mass percent of solvent was 64%, the mass percent of alkyl ketene dimer was 8%, and the mass percent of calcium stearate was 10%.

Example 7:

the embodiment provides a starch-based temporary plugging agent for fracturing, which comprises calcium stearate and a starch modifier, wherein the calcium stearate accounts for 8% of the total mass of a starch modifier suspension and the calcium stearate, and the starch modifier suspension is a mixed solution of the starch modifier and a solvent.

The preparation process comprises the following steps:

firstly, adding 15g of starch and 72g of acetone into a three-neck flask, fully stirring for 2 hours at 20 ℃ to obtain a starch suspension, then heating to 50 ℃, slowly dropwise adding 5g of AKD by using a separating funnel under reflux condensation, and after dropwise adding, continuously reacting for 2 hours at 50 ℃ to obtain a starch modified substance suspension.

And secondly, adding 8g of calcium stearate into the suspension of the starch modifier, fully stirring for 1h, centrifuging the obtained suspension, taking the precipitate, and drying to obtain the starch-based temporary plugging agent for fracturing.

In this example, the mass percent of starch was 15%, the mass percent of solvent was 72%, the mass percent of alkyl ketene dimer was 5%, and the mass percent of calcium stearate was 8%.

And (3) performance measurement:

1. characterization of the intensity

In order to characterize the strength of the starch-based fracturing temporary plugging agent, the plugging strength of the starch-based fracturing temporary plugging agent synthesized in example 4 was tested by using artificial fracture cores with different permeabilities, the mass concentration of the starch-based fracturing temporary plugging agent was 5wt%, and the experimental results are shown in table 1.

Table 1 plugging strength test results

As can be seen from the data in Table 1, the plugging strength of the temporary plugging agent slightly decreases with the increase of the permeability of the core, and when the permeability isWhen the core length is 6.51cm, the breakthrough pressure is 3.7Mpa, and the breakthrough pressure gradient is 56.8 Mpa.m^-1The starch-based fracturing temporary plugging agent can effectively plug cracks.

2. Temporary plugging and unblocking performance

The starch-based fracturing temporary plugging agent synthesized in example 4 was tested for temporary plugging performance by using artificial fracture cores of different permeabilities, the mass concentration of the starch-based fracturing temporary plugging agent was 5wt%, after temporary plugging, formation water was used for scouring, and the plugging removal performance after scouring was determined, with the experimental results shown in table 2.

TABLE 2 temporary plugging and deblocking test results

As can be seen from Table 2, the plugging rate of the starch-based temporary fracturing plugging agent on the rock core can reach more than 90%, and the plugging removal rate can also reach more than 90%, which indicates that the starch-based temporary fracturing plugging agent has good plugging and plugging removal capabilities.

The blockage removal principle is as follows:

after the temporary plugging agent is injected underground, ester can be hydrolyzed under the high-temperature condition of the underground, the hydrophilic capacity of molecules is enhanced after hydrolysis, the solubility is increased, and the blockage removal is facilitated.

In conclusion, compared with the traditional starch fracturing temporary plugging agent, the starch fracturing temporary plugging agent provided by the invention fully utilizes the tackifying property of the starch, modifies the starch while protecting the starch, improves the hydrophobicity of the modified starch molecule surface, reduces the degradation speed, fully utilizes the polymer structure to plug cracks, improves the physical strength by doping insoluble solid particles, further improves the temporary plugging capability, and is simple and feasible in method.

The above examples are merely illustrative of the present invention and should not be construed as limiting the scope of the invention, which is intended to be covered by the claims and any design similar or equivalent to the scope of the invention.