Environmentally friendly autogenous acid and preparation method and use method thereof

Abstract

The invention discloses an environment-friendly self-generated acid and a preparation method and a use method thereof, belonging to the technical field of oilfield chemistry. The environment-friendly self-generated acid comprises an acid generator composition and a dosing aqueous solution, wherein the acid generator composition comprises the following raw material components: 30 to 70 parts of deionized water, 20 to 30 parts of ethyl lactate, 10 to 15 parts of methyl lactate, 5 to 10 parts of trimethyl citrate, 5 to 10 parts of N-methylene chitosan phosphate, 2 to 5 parts of chitosan oligosaccharides, and 3 to 5 parts of sodium tripolyphosphate; the dosing aqueous solution comprises hexadecyl trimethyl ammonium bromide. The acid generator composition and the dosing aqueous solution are separated from each other before acidification construction, and the two are directly pumped into the well after being mixed in a predetermined ratio during the acidification construction process. The acid generator composition has stable performance before being mixed with the dosing aqueous solution, is not easy to be oxidized and hydrolyzed, can quickly generate acid after mixing, and has a good acidification effect after being used on site.

Description

Technical Field

[0001] The invention belongs to the technical field of oilfield chemistry, and in particular relates to an environmentally friendly autogenous acid and a preparation method and a use method thereof. Background Art

[0002] Autogenous acid technology is a method of self-generating acidic substances through chemical reactions in the reservoir environment. This method usually uses precursor compounds that can react under specific conditions to slowly release acid in the underground environment, thereby gradually dissolving the rock and increasing the permeability of oil and gas. The composition and / or proportion of the autogenous acid system used varies according to different reservoir conditions. For example, some systems mainly use polyformaldehyde and ammonium chloride, while other systems may add additional organic acid salts or amines to improve the acidizing effect. Some autogenous acids are specially customized for medium and low temperature reservoirs, while others are suitable for high temperature deep well environments, and even specifically for carbonate or sandstone reservoirs; some autogenous acid technologies use a composite method to combine autogenous acid with other acidizing fluids and gel acid systems to improve the overall effect and scope of application.

[0003] In recent years, for environmental protection and other reasons, organic carboxylic acid esters have been promoted for use. However, ethyl acetate, ethyl formate, etc. are currently used as the main acid generators on site. These acid generators have good acid generation effects and can efficiently produce acidic substances under specific conditions to meet the acidification needs of oil field mining and other operations. They also have low production costs and good thermal stability. However, these acid generators have a low flash point, which means that there is a risk of flammability and explosion when used in a field environment.

[0004] At present, some autogenous acids use methyl lactate, ethyl lactate and the like as acid generators. Although these acid generators have relatively high flash points and improved safety, their acid generation rate is not as good as that of ethyl acetate, ethyl formate and other acid generators. In addition, for this type of autogenous acid, the construction is generally carried out on site after temporary compounding of multiple single agents. Since the acid generation system is too complex and involves the precise proportion of multiple components, there are problems of operational difficulty and high cost when mixing. Moreover, compared with ethyl acetate and ethyl formate, the molecular structure of methyl lactate and ethyl lactate acid generators contains active functional groups hydroxyl groups in addition to ester groups, which makes their structure unstable. In the compounding process, the acid generator is exposed to the air and a large amount of water is added. Therefore, if it cannot be injected into the well in time after the acid is mixed, it will face the risk of oxidation and hydrolysis, which will affect the final acidification effect. In fact, there are many uncertain factors in on-site construction. For example, during the acid fracturing construction process, accidents (such as acid fracturing equipment failure, packer failure, pipe leakage, etc.) often occur due to inaccurate judgment of the situation, insufficient analysis, or improper construction preparation, command and operation, resulting in interruption of acid fracturing construction. The interruption time can be as short as a few hours or as long as more than ten days or even longer. In this case, the effect of acidizing is difficult to guarantee.

[0005] In view of this, it is necessary to further improve the existing technology and provide a self-generated acid system that is safer, more stable, has a good acid-generating effect and is convenient for construction and operation. Summary of the invention

[0006] In view of the problems existing in the prior art, the present invention provides an environmentally friendly autogenous acid and a preparation method and a use method thereof, the purpose of which is to solve at least one of the above problems.

[0007] The present invention achieves its technical purpose through the following technical solutions:

[0008] An environmentally friendly self-generated acid comprises an acid generator composition, wherein the acid generator composition comprises the following raw material components by weight: 30-70 parts of deionized water, 20-30 parts of ethyl lactate, 10-15 parts of methyl lactate, 5-10 parts of trimethyl citrate, 5-10 parts of N-methylene chitosan phosphate, 2-5 parts of chitosan oligosaccharide, and 3-5 parts of sodium tripolyphosphate.

[0009] Furthermore, the environmentally friendly autogenous acid also includes a prepared aqueous solution, which is a solution prepared by adding cetyltrimethylammonium bromide to clean water, wherein the mass fraction of cetyltrimethylammonium bromide in the prepared aqueous solution is 0.1% to 0.2%; wherein the acid generator composition accounts for 10% to 30% by weight of the prepared aqueous solution.

[0010] Preferably, the acid generator composition and the aqueous solution are separated from each other before the acidification construction, and during the acidification construction process, the two are mixed in a predetermined ratio and then directly pumped into the well.

[0011] A method for using an environmentally friendly autogenous acid, comprising at least:

[0012] Step 1: preparing the acid generating agent composition in a production plant;

[0013] Step 2: preparing the aqueous solution at the acidification construction site;

[0014] Step 3: During the acidification construction process where acid solution needs to be injected into the well, the acid generating agent composition of step 1 is mixed with the prepared aqueous solution of step 2 and then directly injected into the well.

[0015] Compared with the prior art, the present invention has at least the following advantages:

[0016] 1. The self-generated acid system of the present invention is more environmentally friendly, and overcomes the environmental pollution problem caused by the addition of formaldehyde and paraformaldehyde in the prior art. Biodegradable ester substances are used as the main acid-generating materials, and green solvent deionized water is used, thereby improving the environmental friendliness of the self-generated acid system; the present invention uses high-flash-point ester substances, and compared with ethyl acetate, ethyl formate, and ethyl acetate used in the prior art, the overall flash point is increased to 50-60° C., which greatly improves safety and prevents flammable and explosive risks;

[0017] 2. The environment-friendly autogenous acid of the present invention is prepared by mixing two parts, the first part is an acid generator composition, and the second part is a dosing aqueous solution. Both parts are highly stable and are not easily hydrolyzed and oxidized in a short time under an open environment. The mixing is performed only when acidification injection is required, and is not performed when the acidification construction is interrupted. This ensures that acid generators such as methyl lactate and ethyl lactate will not deteriorate due to temporary accident interruptions when used on site, thereby affecting the subsequent acidification effect. In addition, since the acid generator composition is prepared in advance, only the dosing aqueous solution and the mixing of the acid generator composition and the dosing aqueous solution need to be performed on the construction site, and the on-site construction is simpler. The autogenous acid system in the prior art requires multiple single agents to be accurately proportioned and temporarily compounded on site before use, which may lead to complex preparation during the construction process, increasing the difficulty and cost of operation.

[0018] 4. The use of N-methylene chitosan phosphate and the like has a passivating effect on the acid generator composition formula, which can effectively reduce its hydrolysis and oxidation rate in an open environment, and the CTAB in the aqueous solution is not affected by N-methylene chitosan phosphate and the like, which can promote the rapid hydrolysis or oxidation of environmentally friendly self-generated acid, making it generate acid quickly, and can greatly improve the acidification effect during acidification, reducing the undesirable situation that N-methylene chitosan phosphate and the like may gel into blocks at high temperatures and then block pores, affecting the acidification effect;

[0019] 5. The use of sodium tripolyphosphate improves the stability of the acid generator composition on the one hand, and on the other hand, during the acidification construction process, it can effectively prevent the organic acid from reacting with calcium and magnesium carbonate to form scale after the self-generated acid enters the formation, thereby ensuring the acidification effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is an operation flow chart of the on-site use of the environmentally friendly autogenous acid in the present invention;

[0021] Figure 2 This is a photograph of marble powder reacted after the environment-friendly autogenous acid of Example 5 of the present invention was tested at 120° C. using the marble powder weight loss method for 8 hours;

[0022] Figure 3 This is a photograph of marble powder reacted after the environment-friendly autogenous acid of Example 5 of the present invention was tested at 140° C. using the marble powder weight loss method for 8 hours;

[0023] Figure 4 This is a photograph of the marble powder reacted after the environment-friendly autogenous acid of Example 5 of the present invention was tested at 160° C. using the marble powder weight loss method for 8 hours;

[0024] Figure 5 This is a comparison of photos before and after the reaction of the environmentally friendly autogenous acid of Example 6 of the present invention with a marble block;

[0025] Figure 6 This is a comparison of photos before and after the reaction of the commonly used acid generator A (formaldehyde + ammonium chloride) on the market with marble blocks;

[0026] Figure 7 This is a comparison of photos before and after the reaction of the commonly used acid generator B (ethyl formate + ammonium chloride) on the market with marble blocks. DETAILED DESCRIPTION

[0027] The technical solution of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] Specifically, the present invention provides an environmentally friendly self-generated acid, which includes an acid generator composition, wherein the acid generator composition includes the following raw material components by weight: 30 to 70 parts of deionized water, 20 to 30 parts of ethyl lactate, 10 to 15 parts of methyl lactate, 5 to 10 parts of trimethyl citrate, 5 to 10 parts of N-methylene chitosan phosphate, 2 to 5 parts of chitosan oligosaccharides, and 3 to 5 parts of sodium tripolyphosphate.

[0029] Furthermore, the environmentally friendly autogenous acid also includes a prepared aqueous solution, which is a solution prepared by adding cetyltrimethylammonium bromide (CTAB) to clean water, wherein the mass fraction of cetyltrimethylammonium bromide in the prepared aqueous solution is 0.1% to 0.2%; the weight ratio of the acid generator composition to the prepared aqueous solution is 10% to 30% (i.e., the acid generator composition: the prepared aqueous solution = 10 to 30: 100).

[0030] In order to better achieve the purpose of the present invention, the acid generator composition and the dosing aqueous solution are separated from each other before the acidification construction, and the two are mixed in a predetermined ratio during the acidification construction and directly pumped into the well. In other words, the acid generator composition and the dosing aqueous solution are prepared independently of each other and can be mixed in proportion when used. Specifically, the preparation of the environmentally friendly autogenous acid is divided into three steps, the first step is the preparation of the acid generator composition, the second step is the preparation of the dosing aqueous solution; the third step is the mixing of the acid generator composition and the dosing aqueous solution.

[0031] More specifically, the preparation of the acid generator composition comprises the following steps (unless otherwise specified, the amount of each component in the preparation method corresponds to the weight portion in the raw material component, which will not be repeated below):

[0032] Step 1: Deionized water is placed in a mixing container, preheated at 45°C for 30 minutes, and stirred at 300 rpm by a stirrer. During the preheating and stirring process, nitrogen is slowly added to the water for 10 minutes to remove dissolved oxygen in the water to avoid the influence of oxidation reaction on subsequent steps;

[0033] Step 2: Keep the preheating temperature, then gradually add ethyl lactate, methyl lactate and trimethyl citrate in sequence, and increase the stirring speed to 500 rpm, and continue stirring for 30 minutes until the trimethyl citrate is completely dissolved to obtain a mixed solution. In step 2, to ensure complete dissolution, the solution is ultrasonically treated for 20 minutes at a frequency of 40 kHz using an ultrasonic treatment device during continuous stirring to eliminate possible tiny undissolved particles;

[0034] Step 3: Slowly add N-methylene chitosan phosphate and chitosan oligosaccharide to the mixed solution, maintain the stirring speed at 500 rpm, and continue stirring for 45 minutes. In step S3, in order to ensure that N-methylene chitosan phosphate and chitosan oligosaccharide are fully combined with other components in the solution, the solution is transferred to a closed reactor and placed in a vacuum environment (about -0.08MPa) for 2 hours to remove bubbles and residual dissolved gases to prevent them from affecting the stability of the system;

[0035] Step 4: slowly introducing sodium tripolyphosphate into the closed reactor, maintaining the stirring speed at 200 rpm to avoid precipitation caused by excessive local concentration;

[0036] Step 5: After all components are mixed, the solution is cooled to room temperature and filtered to obtain an acid generator composition. Then, under the protection of an inert gas (such as nitrogen), the acid generator composition is quickly placed in a pre-sterilized sealed container, and polydimethylsiloxane is added at a ratio of 1% of the total weight of the acid generator composition in the sealed container for oil sealing to ensure that the product does not volatilize. At the same time, 5 to 10 ml of inert gas is added to the sealed container to isolate the acid generator composition from the outside atmosphere to prevent degradation problems that may occur due to oxidation during long-term storage, thereby completing the encapsulation of the acid generator composition.

[0037] It should be noted that in the present invention, the preparation of the acid generator composition is completed in the production plant (not at the acidification construction site). Due to the packaging operation and the effects of N-methylene chitosan phosphate and chitosan oligosaccharide, ethyl lactate, methyl lactate and trimethyl citrate hardly undergo hydrolysis and oxidation reactions during storage (it should be understood that they are within the shelf life). The storage conditions of the acid generator composition are preferably: stored at 20-25°C and avoid direct sunlight or high temperature environment.

[0038] It should be further explained that the preparation aqueous solution is prepared directly at the construction site, and the general steps are: first, weigh a predetermined amount of hexadecyltrimethylammonium bromide, add it to the preparation tank, stir and mix evenly, and obtain a preparation aqueous solution of the corresponding mass fraction. The preparation method is very simple, and there are many related preparation methods in the prior art, which will not be repeated here.

[0039] At the construction site, when acidification construction is required, the acid generator composition is directly mixed with the preparation aqueous solution in a predetermined ratio and then injected into the well.

[0040] The following are some embodiments of the experimental tests of the present invention. Since the acid generator composition and the liquid preparation aqueous solution of the present invention are prepared separately, the two are separated from each other during storage and are mixed only when injected during acidification construction. Therefore, in these embodiments, the acid generator composition that plays a major role in acid generation is tested separately, and the environmentally friendly autogenous acid generated by mixing the acid generator composition with the liquid preparation aqueous solution is tested separately (the liquid preparation aqueous solution is a single-dose solution, its performance is stable, and it is a known technology, so it is not tested).

[0041] Embodiment 1

[0042] An acid generator composition comprises the following raw material components by weight: 30 parts of deionized water, 20 parts of ethyl lactate, 10 parts of methyl lactate, 5 parts of trimethyl citrate, 5 parts of N-methylene chitosan phosphate, 2 parts of chitosan oligosaccharide, and 3 parts of sodium tripolyphosphate.

[0043] An environmentally friendly autogenous acid comprises a mixed aqueous solution and an acid generator composition provided in this embodiment, wherein the aqueous solution is a solution prepared by adding cetyltrimethylammonium bromide (CTAB) to clean water, and the mass fraction of cetyltrimethylammonium bromide in the aqueous solution is 0.1%; and the weight ratio of the acid generator composition to the aqueous solution is 20%.

[0044] The corresponding preparation method is as mentioned above and will not be described again here.

[0045] Embodiment 2

[0046] An acid generator composition comprises the following raw material components by weight: 70 parts of deionized water, 30 parts of ethyl lactate, 15 parts of methyl lactate, 10 parts of trimethyl citrate, 10 parts of N-methylene chitosan phosphate, 5 parts of chitosan oligosaccharide, and 5 parts of sodium tripolyphosphate.

[0047] An environmentally friendly autogenous acid comprises a mixed aqueous solution and an acid generator composition provided in this embodiment, wherein the aqueous solution is a solution prepared by adding cetyltrimethylammonium bromide (CTAB) to clean water, and the mass fraction of cetyltrimethylammonium bromide in the aqueous solution is 0.1%; and the weight ratio of the acid generator composition to the aqueous solution is 20%.

[0048] The corresponding preparation method is as mentioned above and will not be described again here.

[0049] Embodiment 3

[0050] An acid generator composition comprises the following raw material components by weight: 50 parts of deionized water, 25 parts of ethyl lactate, 12 parts of methyl lactate, 8 parts of trimethyl citrate, 8 parts of N-methylene chitosan phosphate, 3 parts of chitosan oligosaccharide, and 4 parts of sodium tripolyphosphate.

[0051] An environmentally friendly autogenous acid comprises a mixed aqueous solution and an acid generator composition provided in this embodiment, wherein the aqueous solution is a solution prepared by adding cetyltrimethylammonium bromide (CTAB) to clean water, and the mass fraction of cetyltrimethylammonium bromide in the aqueous solution is 0.1%; and the weight ratio of the acid generator composition to the aqueous solution is 20%.

[0052] The corresponding preparation method is as mentioned above and will not be described again here.

[0053] Embodiment 4

[0054] The acid generator composition in this embodiment is the same as the acid generator composition in Example 3 (the components and proportions are the same).

[0055] The environmentally friendly autogenous acid in this embodiment includes a mixed preparation aqueous solution and the acid generator composition provided in this embodiment, wherein the preparation aqueous solution is a solution prepared by adding cetyltrimethylammonium bromide (CTAB) to clean water, and the mass fraction of cetyltrimethylammonium bromide in the preparation aqueous solution is 0.2%; the weight ratio of the acid generator composition used for mixing to the preparation aqueous solution is 20%.

[0056] The corresponding preparation method is as mentioned above and will not be described again here.

[0057] Embodiment 5

[0058] The acid generator composition in this embodiment is the same as the acid generator composition in Example 3 (the components and proportions are the same).

[0059] The environmentally friendly autogenous acid in this embodiment includes a mixed preparation aqueous solution and the acid generator composition provided in this embodiment, wherein the preparation aqueous solution is a solution prepared by adding cetyltrimethylammonium bromide (CTAB) to clean water, and the mass fraction of cetyltrimethylammonium bromide in the preparation aqueous solution is 0.2%; the weight ratio of the acid generator composition used for mixing to the preparation aqueous solution is 10%.

[0060] The corresponding preparation method is as mentioned above and will not be described again here.

[0061] Embodiment 6

[0062] The acid generator composition in this embodiment is the same as the acid generator composition in Example 3 (the components and proportions are the same).

[0063] The environmentally friendly autogenous acid in this embodiment includes a mixed preparation aqueous solution and the acid generator composition provided in this embodiment, wherein the preparation aqueous solution is a solution prepared by adding cetyltrimethylammonium bromide (CTAB) to clean water, and the mass fraction of cetyltrimethylammonium bromide in the preparation aqueous solution is 0.2%; the weight ratio of the acid generator composition to the preparation aqueous solution used for mixing is 30%.

[0064] The corresponding preparation method is as mentioned above and will not be described again here.

[0065] Comparative Example 1

[0066] The acid generator composition and the environmentally friendly autogenous acid of Comparative Example 1 refer to Example 3, except that the acid generator composition does not contain N-methylene chitosan phosphate; the remaining components and proportions are the same as those of Example 3.

[0067] Comparative Example 2

[0068] The acid generator composition and the environmentally friendly autogenous acid of Comparative Example 2 refer to Example 3, except that the acid generator composition does not contain chitosan oligosaccharide; the remaining components and proportions are the same as those of Example 3.

[0069] Comparative Example 3

[0070] The acid generator composition and the environmentally friendly autogenous acid of Comparative Example 3 refer to Example 3, except that the acid generator composition contains neither N-methylene chitosan phosphate nor chitosan oligosaccharide; the remaining components and proportions are the same as those of Example 3.

[0071] Comparative Example 4

[0072] The acid generator composition and the environmentally friendly autogenous acid of Comparative Example 4 refer to Example 3, except that the acid generator composition does not contain sodium tripolyphosphate; the remaining components and proportions are the same as those of Example 3.

[0073] Comparative Example 5

[0074] The acid generator composition and the environmentally friendly autogenous acid of Comparative Example 5 refer to Example 3, except that the acid generator composition contains neither N-methylene chitosan phosphate nor chitosan oligosaccharide, but contains 11 parts by weight of the iron ion stabilizer disodium ethylenediaminetetraacetate; the remaining components and proportions are the same as those of Example 3.

[0075] Comparative Example 6

[0076] The acid generator composition and the environmentally friendly autogenous acid of Comparative Example 6 refer to Example 3, except that cetyltrimethylammonium bromide (CTAB) is not added to the aqueous solution of the solution in Comparative Example 6, that is, clean water is used to mix the acid generator composition, and the weight ratio of the acid generator composition to clean water used for mixing is 20%; the remaining components and proportions are the same as those in Example 3.

[0077] Performance Test:

[0078] During the acidification construction, there will be acidification interruptions due to various factors. Since the existing acidification construction usually produces acid solution by compounding on site, during the compounding process, each component will be exposed to the air one by one and put into water to form acid solution. For acid generators such as ethyl lactate and methyl lactate that are easily hydrolyzed and oxidized, if the existing one-time compounding method is used, when the interruption time is long, the compounded acid solution will face the risk of oxidation and hydrolysis and affect the final acidification effect. The present invention also uses acid generators such as ethyl lactate and methyl lactate, so it is necessary to test their stability in an air environment. Exemplary stability tests include pH determination, mass spectrometry test, OIT test, etc.; since the acid generator composition in the present invention plays a major role in acid generation and is prepared separately, it will only be mixed with the preparation aqueous solution when acid injection is performed at the acidification construction site, and it will be unpacked for preparation before acid injection, that is, when using the formulation of the present invention, the component that is easily exposed to the air is the acid generator composition, rather than the environmentally friendly self-generated acid; therefore, here we conduct a stability test on the acid generator composition, specifically, they (taking the same mass) are exposed to an environment of 25°C, and the pH changes after being exposed for 15 days and 30 days are tested. Among them, since the acid generator compositions of Example 4, Example 5, Example 6 and Comparative Example 6 are the same as the acid generator composition of Example 3, only one test is performed. In addition, the environmentally friendly autogenous acid is a mixed solution, and its components are similar to the existing compound acid solution. Here, it is exposed in the same way to test its pH change as a reference for performance changes. The following Table 1 shows the test results:

[0079] Table 1: PH test results

[0080]

[0081] Note: The acid generator composition and the environmentally friendly autogenous acid were temporarily compounded during the experiment, and the pH value was obtained by measuring with a pH meter.

[0082] As can be seen from Table 1, for the acid generator composition of the present invention (see Examples 1 to 6), the pH value changes little when it is left open for a long time (the pH value is still higher than 6 when it is left open for 30 days), which indicates that the proportion of hydrolysis and oxidation of its raw material components is small when it is left open. From Comparative Example 1, it can be seen that when N-methylene chitosan phosphate is not added to the acid generator composition, the pH value decreases rapidly over time, especially in Comparative Example 3 which contains neither N-methylene chitosan phosphate nor chitosan oligosaccharides; in Comparative Example 2, the pH value decreases slowly but faster than that of Examples 1 to 6, indicating that chitosan oligosaccharides also have a certain promoting effect on the stability of the acid generator composition, which may be due to the fact that chitosan oligosaccharides themselves have certain acidity regulation and antioxidant effects; and when N-methylene chitosan phosphate is used together with chitosan oligosaccharides, the two act synergistically to further improve the stability of the acid generator composition. In Comparative Example 4, sodium tripolyphosphate was not added, resulting in a decrease in the initial pH value of the acid generator composition, resulting in a faster hydrolysis and oxidation rate during the open process than in Examples 1 to 6, indicating that sodium tripolyphosphate also has a certain promoting effect on the stability of the entire acid generator composition (this promotion may be affected by pH); in Comparative Example 5, the iron ion stabilizer disodium ethylenediaminetetraacetate was used to replace N-methylene chitosan phosphate and chitosan oligosaccharides. It was found that the pH value dropped rapidly and the hydrolysis and oxidation were almost unable to be inhibited. This may be because the introduction of disodium ethylenediaminetetraacetate reduced the initial pH value of the acid generator composition. At the same time, disodium ethylenediaminetetraacetate has a limited promoting effect on the stability of the acid generator composition.

[0083] In addition, it should be noted that the reason why N-methylene chitosan phosphate plays an important role in maintaining the stability of the acid generator composition of the present invention may be because: 1. N-methylene chitosan phosphate is an anionic polymer, and the phosphate groups on its molecular chain can interact with other groups to form a stable network structure between molecules. This structure can enhance the intermolecular forces in the system, thereby improving the stability of the acid generator composition, and it has good hydrophilicity and dispersibility, can be effectively dispersed in the solution, and form a uniform mixed system with other components to prevent the aggregation or precipitation of the components, thereby improving the dispersion stability of the system; 2. N-methylene chitosan phosphate and chitosan oligosaccharide have good thickening properties. In the formula, since the amount of deionized water is relatively small, the viscosity of the solution of the acid generator composition is higher and the fluidity is lower. This high viscosity environment reduces the chance of internal components contacting with air and reduces the risk of oxidation reaction, thereby helping to maintain the stability of the system. In addition, high viscosity can prevent precipitation or separation of components, ensure uniform distribution of components, and maintain product uniformity; 3. The molecules of N-methylene chitosan phosphate contain larger methylene phosphate groups, which occupy a certain position in space and form steric hindrance. When other component molecules try to approach N-methylene chitosan phosphate, they will be hindered by this steric hindrance, thereby effectively preventing direct contact and interaction between molecules of different components and improving the dispersion stability of the system.

[0084] Further, in an open environment, the pH values ​​of the environmentally friendly autogenous acids of Examples 1 to 6 in Table 1 all dropped rapidly, which shows that when the acid generator composition is mixed with the aqueous solution of the dosing liquid, due to the introduction of a large amount of water and CTAB in the water, the mixed solution is no longer as stable as the acid generator composition. Therefore, at the construction site, the environmentally friendly autogenous acid also needs to be injected into the well in time. In addition, the pH values ​​of Comparative Examples 1 to 5 all dropped rapidly, but the pH value of the environmentally friendly autogenous acid in Comparative Example 6 dropped significantly slower than that of Comparative Examples 1 to 5. It can be seen from this that the CTAB in the aqueous solution of the dosing liquid has a positive promoting effect on the hydrolysis or oxidation of the environmentally friendly autogenous acid, and even in the presence of stabilizers such as N-methylene chitosan phosphate and chitosan oligosaccharides, this promotion is still not affected; this performance helps to ensure that the subsequent acid generation rate is sufficient after the acid generator composition is mixed with the aqueous solution of the dosing liquid.

[0085] In order to verify the acid-generating capacity, we took the same mass of the environmentally friendly autogenous acid of Example 5 and the autogenous acid of Comparative Example 6 to test the acid-generating concentration. Specifically, the marble powder (calcium carbonate) weight loss method was used to test the acid concentration of 8 h in an environment of 120°C, and the effective hydrogen ion concentration (in terms of HCL) after 8h was 1.01% (Example 5) and 0.24% (Comparative Example 6), respectively. This further illustrates that the introduction of CTAB can significantly promote the rapid acid generation of environmentally friendly autogenous acid in a high-temperature formation environment, and in the presence of the stabilizing components composed of N-methylene chitosan phosphate and chitosan oligosaccharide, it still has a high acid generation promotion effect, which may be due to the different action mechanisms of CTAB and N-methylene chitosan phosphate, and the two do not interfere with each other (or interfere very little); in addition, after the experiment, we conducted a microscopic magnification observation on the marble powder remaining in the reaction and found that a certain amount of gelling material was attached to its surface (possibly caused by N-methylene chitosan phosphate, etc.), the environmentally friendly autogenous acid of Example 5 corresponds to a network structure, while the comparative example 6 corresponds to an irregular mass structure, and this structural difference may reflect the different ways in which the two autogenous acids interact with the marble powder during the reaction, which may have different effects on the acidification effect. On this basis, we used the environmentally friendly autogenous acid of Example 5 and the autogenous acid of Comparative Example 6 to acidify two oil and gas wells with the same production layer, close geographical location but not affecting each other. Specifically, the Tuzi 3 well (environmentally friendly autogenous acid of Example 5) and Tuzi 2 well (autogenous acid of Comparative Example 6) of the Tuziluo gas field project of the Tarim Oilfield were transformed. The production capacity of these two wells has dropped significantly after long-term production, and the production status of the two wells is very close, which is suitable for acidification comparison. After the acidification construction is completed, the two wells increased production by 247% and 36% respectively (both calculated based on the daily gas production increment after acidification stable production). Among them, the production increase effect of Tuzi 2 well is not obvious, which may be due to insufficient acid production capacity on the one hand, and on the other hand, it may be due to the influence of its gelation. Therefore, the present invention introduces CTAB into autogenous acid to make it interact with N-methylene chitosan phosphate, chitosan oligosaccharide, etc., thereby improving the acidification effect.

[0086] The following are some brief descriptions of the acid-generating mechanism of the environmentally friendly autogenous acid of the present invention:

[0087] In the formula, ethyl lactate, methyl lactate, and trimethyl citrate are acid precursors and are the main sources of acidic substances. During the acidification process, they generate acids through hydrolysis or other chemical reactions to play an acidifying role. The following is the reaction equation:

[0088] Hydrolysis reaction of methyl lactate:

[0089]

[0090] Hydrolysis reaction of ethyl lactate:

[0091]

[0092] Hydrolysis reaction of trimethyl citrate:

[0093]

[0094] Among them, ethyl lactate and methyl lactate decompose under the action of water to generate the corresponding organic acid lactic acid and alcohols ethanol and methanol, while trimethyl citrate generates citric acid and methanol. Lactic acid and citric acid release hydrogen ions H⁺ in the solution, thereby lowering the pH value of the solution and achieving the effect of acid generation. When trimethyl citrate is added, the citric acid generated by it avoids the scaling and precipitation of the generated calcium and magnesium lactate salts through chelation during the acid-rock reaction, and captures the complexed part of calcium and magnesium ions in advance.

[0095] Furthermore, the use of N-methylene chitosan phosphate and chitosan oligosaccharide can maintain the stability of the acid generator composition in an open environment, which is equivalent to the passivation component of the self-generated acid. After adding the aqueous solution, it can not affect the acid generation performance under the action of CTAB and a large amount of water, ensuring sufficient acid generation capacity and acidification effect. CTAB is similar to an activating component, which eliminates the above-mentioned passivation effect to a certain extent, prevents the gelation agglomeration phenomenon, and makes the N-methylene chitosan phosphate gelled at high temperature in the acidification construction networked, ensuring that the acid enters the formation smoothly. In the process of acidification, N-methylene chitosan phosphate can also play a role in corrosion inhibition, preventing the generated acid from adversely affecting the downhole tubing.

[0096] Furthermore, in addition to its pH regulation function to maintain the stability of the acid generator composition, sodium tripolyphosphate also acts as an anti-precipitant, which can effectively prevent organic acids from reacting with calcium and magnesium carbonate to form scale after the autogenerated acid enters the formation (when organic acids react with calcium carbonate, soluble organic acid calcium salts are usually generated, but if the reaction conditions are inappropriate or the concentration of the organic acid is insufficient, some incompletely reacted calcium carbonate may precipitate in solid form to form scale). This scale usually forms solid particles, which precipitate or adhere to the production channel of the formation, thereby blocking the channel and affecting the production of oil and gas. Sodium tripolyphosphate forms soluble complexes with metal ions such as calcium and magnesium to prevent these ions from reacting with organic acids to form insoluble precipitates. In addition, its complexing ability can also help disperse the precipitated particles that have already formed, further reducing the risk of clogging.

[0097] In order to further understand the acid-generating capacity of the environmentally friendly autogenous acid of the present invention, we also conducted the following experiments:

[0098] 1. The environmentally friendly autogenous acid of Example 5 (10% acid generator composition + 90% aqueous solution) was used to test the acid generating capacity at different temperatures. Specifically, the marble powder (calcium carbonate) weight loss method was used to test the acid generating concentration at 120°C, 140°C, and 160°C for 8 hours. The results are as follows:

[0099] Table 2: Acid concentration table

[0100]

[0101] It can be seen from Table 2 that at a formation temperature of 160°C, the effective hydrogen ion concentration reaches the highest, indicating that the environmentally friendly autogenous acid of the present invention is suitable for use in a high temperature environment. Figures 2 to 4 .

[0102] In order to prove that the environmentally friendly autogenous acid of the present invention has good etching and scale inhibition effects, the following verification is performed:

[0103] The common autogenous acid materials on the market are compared with the environmentally friendly autogenous acid materials of the patent formula. Table 3 shows the comparison results. The formula of the patent adopts the environmentally friendly autogenous acid of Example 6 (30% acid generator composition + 70% liquid preparation aqueous solution). The etching effect of autogenous acid on marble is tested at 140°C. The results are as follows:

[0104] Table 3: Etching effect comparison table:

[0105]

[0106] Photos of the reaction before and after Figures 5 to 7 ; From Table 3 and Appendix Figure 5 To Attachment Figure 7 It can be seen that under the same formula concentration, the acid concentration of each acid generator reacting with calcium carbonate powder is equivalent, but compared with the acid concentration of etching marble blocks, the etching of marble blocks by this patented product is more obvious and the acid concentration is higher. The reason is that the organic acid calcium and magnesium compounds generated by other acid generators have a strong scaling tendency, which will quickly form a covering layer on the surface of calcium carbonate to hinder the generation of acid-rock reaction, resulting in a slowdown in the subsequent reaction rate. The environmentally friendly self-generated acid of this patent adds stabilizers and anti-precipitants. The stabilizer can prevent stratification and anti-precipitation, and the chelation of citric acid and phosphoric acid can stabilize calcium and magnesium ions. The solubility of calcium lactate varies greatly with temperature. It is difficult to dissolve at room temperature and easily soluble at high temperature. Although the calcium lactate generated by the reaction in the formation is in a soluble state, during the flowback process, calcium lactate will easily precipitate as the fracturing fluid gradually cools down, so a scale inhibitor is needed.

[0107] According to the above content, the present invention also relates to a method for using an environmentally friendly autogenous acid, which specifically comprises the following steps:

[0108] Step 1, preparation of an acid generating agent composition;

[0109] Step 2, preparation of the aqueous solution;

[0110] Step 3: During the acidification construction process where acid solution needs to be injected into the well, the acid generating agent composition of step 1 is mixed with the prepared aqueous solution of step 2.

[0111] Among them, the preparation of the acid generator composition is completed in the production plant, and the preparation of the aqueous solution is completed at the construction site. The specific preparation method has been described in the previous text and will not be repeated here.

[0112] Acid solution preparation is required before acidification construction. At this time, the acid generator composition prepared in the production plant needs to be unpacked at the construction site and introduced into the storage tank of the acid generator composition. During this process, the acid generator composition will be exposed to a large amount of oxygen. Since the acid generator composition of the present invention has good stability and is not mixed with a large amount of water at this time, it can maintain stable performance in a short period of time (for example, within 1 month). Even if the acidification construction preparation work is completed or the acidification construction is interrupted due to various factors during the acidification construction, the acid generator composition will not have the risk of deterioration, so the subsequent acidification effect can be ensured.

[0113] For details, see Figure 1 At the construction site, the acid generator composition is introduced into and stored in a storage tank of the acid generator composition, and the dosing aqueous solution is prepared and stored in a storage tank of the dosing aqueous solution. The outlets of the two storage tanks are respectively provided with a first pump and a second pump, and the first pump and the second pump are connected to the controller in communication, and the controller can control the outlet flow of the first pump and the second pump, and then the acid generator composition and the dosing aqueous solution are mixed according to a predetermined ratio. This proportional control method is very common in the prior art and will not be repeated. Further, in order to ensure that the acid generator composition and the dosing aqueous solution are fully mixed, other self-mixers, agitators, etc. can also be used. Preferably, the mixed environmentally friendly autogenous acid that meets the requirements is introduced into the buffer container, and the fracturing pump vehicle group directly pumps the environmentally friendly autogenous acid from the buffer container into the well to implement the acidification operation. When the acidification construction is interrupted midway, due to the small size of the buffer container, there is only a small amount of environmentally friendly autogenous acid in it, and a large amount of acid generator composition is still stored in its storage tank, maintaining its stable performance, so it will not affect the subsequent acidification construction. In addition, since the acid generator composition and the preparation aqueous solution of the present invention are close to neutral, there is no requirement for the anti-corrosion ability of the storage tanks, which simplifies the equipment requirements on site. During construction, only simple mixing is required and the fracturing vehicle group is directly put into the well, making the preparation construction extremely convenient.

[0114] It should be understood that "comprising" as used herein with respect to the acid generator composition and the environmentally friendly autogenous acid includes the approach of "consisting of".

[0115] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical solutions and concepts of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. An environmentally friendly autogenous acid, comprising an acid generator composition, characterized in that: The acid generator composition comprises the following raw material components by weight: 30-70 parts of deionized water, 20-30 parts of ethyl lactate, 10-15 parts of methyl lactate, 5-10 parts of trimethyl citrate, 5-10 parts of N-methylene chitosan phosphate, 2-5 parts of chitosan oligosaccharide, and 3-5 parts of sodium tripolyphosphate; The environmentally friendly autogenous acid further comprises a prepared aqueous solution, wherein the prepared aqueous solution is a solution prepared by adding hexadecyltrimethylammonium bromide to clean water; The acid generator composition and the liquid preparation aqueous solution are separated from each other before the acidification construction, and are directly pumped into the well after being mixed in a predetermined proportion during the acidification construction process.

2. An environmentally friendly autogenous acid as claimed in claim 1, characterized in that: The mass fraction of hexadecyltrimethylammonium bromide in the aqueous solution is 0.1% to 0.2%.

3. An environmentally friendly autogenous acid as claimed in claim 1, characterized in that: The predetermined ratio means that the acid generator composition accounts for 10% to 30% by weight of the aqueous solution.

4. The method for using an environmentally friendly autogenous acid according to claim 1, characterized in that: The method comprises the following steps: Step 1: preparing the acid generating agent composition in a production plant; Step 2: preparing the aqueous solution at the acidification construction site; Step 3: During the acidification construction process where acid solution needs to be injected into the well, the acid generating agent composition of step 1 is mixed with the prepared aqueous solution of step 2 and then injected into the well.

5. The method for using an environmentally friendly autogenous acid according to claim 4, characterized in that: In step three, at the acidification construction site, the acid generator composition is introduced and stored in a storage tank for the acid generator composition, the preparation aqueous solution is prepared and stored in a storage tank for the preparation aqueous solution, and the acid generator composition and the preparation aqueous solution are mixed and directly pumped into the well.

6. The method for using an environmentally friendly autogenous acid according to claim 5, characterized in that: A first pump is provided at the outlet of the storage tank of the acid generator composition, and a second pump is provided at the outlet of the storage tank of the preparation aqueous solution. The acid generator composition and the preparation aqueous solution are mixed in a predetermined ratio by adjusting the outlet flow rates of the first pump and the second pump.

7. The method for using an environmentally friendly autogenous acid according to claim 6, characterized in that: The environmentally friendly autogenous acid obtained after mixing in a predetermined ratio is introduced into a buffer container, and then the environmentally friendly autogenous acid from the buffer container is directly pumped into the well by a fracturing pump truck.

8. A method for preparing an environmentally friendly autogenous acid, for preparing the environmentally friendly autogenous acid according to any one of claims 1 to 2, characterized in that: The environmentally friendly self-generated acid-generating agent composition is prepared by the following steps: Step 1: Deionized water is placed in a mixing container, preheated at 45°C for 30 minutes, and stirred at 300 rpm by a stirrer. During the preheating and stirring process, nitrogen is slowly added to the water for 10 minutes to remove dissolved oxygen in the water to avoid the influence of oxidation reaction on subsequent steps; Step 2: maintaining the preheating temperature, then gradually adding ethyl lactate, methyl lactate and trimethyl citrate in sequence, and increasing the stirring speed to 500 rpm, stirring for 30 minutes until the trimethyl citrate is completely dissolved to obtain a mixed solution; Step 3: Slowly add N-methylene chitosan phosphate and chitosan oligosaccharide to the mixed solution obtained in step 2, and maintain the stirring speed at 500 rpm, and continue stirring for 45 minutes; during this process, transfer the solution to a closed reactor and stand it for 2 hours under a vacuum environment to remove bubbles and residual dissolved gas; Step 4: Slowly introduce sodium tripolyphosphate into the closed reactor, maintain the stirring speed at 200 rpm to avoid precipitation caused by excessive local concentration; Step 5: After all components are mixed, the solution is cooled to room temperature and filtered to obtain an acid generator composition. Then, under the protection of an inert gas, the acid generator composition is quickly placed in a pre-sterilized sealed container, and polydimethylsiloxane is added at a ratio of 1% of the total weight of the acid generator composition in the sealed container for oil sealing to ensure that the product does not volatilize. At the same time, 5 to 10 ml of inert gas is added to the sealed container to isolate the acid generator composition from the outside atmosphere, thereby completing the encapsulation of the acid generator composition.

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