An environmentally friendly well wall stabilizer and its preparation method and application

Abstract

The present invention provides an environmentally friendly well wall stabilizer and a preparation method and application thereof. The preparation method of the well wall stabilizer of the present invention comprises the steps of: dissolving polyvinyl alcohol in deionized water to obtain a polyvinyl alcohol aqueous solution; fully dispersing saikosaponin in the polyvinyl alcohol aqueous solution and adjusting the pH to alkaline; reacting under stirring conditions; adjusting the pH to neutral and drying to obtain an environmentally friendly well wall stabilizer. The preparation method of the present invention is simple, low-cost and environmentally friendly. The well wall stabilizer of the present invention can effectively inhibit the hydration of shale, and at the same time has an excellent bonding and solidifying effect, can be used in fractured shale formations, and has good well wall stability.

Description

Technical Field

[0001] The invention relates to an environmentally friendly well wall stabilizer and a preparation method and application thereof, belonging to the technical field of drilling. Background Art

[0002] With the exploration and development of shale gas, wellbore instability accidents frequently occur during drilling, especially in fractured shale formations, where long horizontal sections are prone to formation collapse, causing significant economic losses and safety issues. Currently, commonly used shale inhibitors mainly maintain wellbore stability by inhibiting the hydration, expansion and dispersion of water-sensitive clay minerals in shale formations, but it is difficult to solve the problem of wellbore collapse in long horizontal sections of drilling in fractured shale formations.

[0003] In recent years, wellbore stabilizers with cementing and wall-fixing properties have become the key to solving the problem of wellbore stability in fractured formations. Chinese patent document CN104177517A discloses a bionic polymer for wellbore stabilization, which contains carboxymethyl chitosan as the main chain and a group derived from dopamine grafted on the main chain. Chinese patent document CN109679598A discloses a strong wall-fixing and anti-collapse water-based drilling fluid, which contains a chemical wall-fixing agent, which is a polymer with dopamine groups grafted on the main chain, and is prepared from branched polyethyleneimine and catechol monomers. However, the above wall-fixing agents containing dopamine are expensive and difficult to achieve industrial application in oil fields; and the performance of inhibiting shale hydration expansion, dispersion and cementing and wall-fixing needs to be improved. Chinese patent document CN114702942A discloses a well wall stabilizer with both inhibitory and wall consolidation functions, including an organic core and a modified nanoparticle coating layer covering at least a portion of the surface of the organic core. However, its synthesis process is too complicated and does not mention environmental issues. At the same time, the inhibition of shale hydration expansion and dispersion performance need to be improved.

[0004] Therefore, there is an urgent need to develop an environmentally friendly, low-cost, and simple-to-prepare wellbore stabilizer that can effectively maintain the stability of the wellbore by inhibiting the hydration expansion and dispersion of water-sensitive clay minerals in shale formations, and can effectively stabilize fractured shale formations through chemical wall consolidation, so as to provide technical support for solving the wellbore stability problem in fractured shale formations. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention provides an environmentally friendly well wall stabilizer and its preparation method and application. The well wall stabilizer of the present invention is prepared by modifying the natural product saikosaponin with polyvinyl alcohol; the preparation method is simple, low-cost and environmentally friendly. The well wall stabilizer of the present invention can effectively inhibit the hydration of shale, and at the same time has an excellent bonding and wall strengthening effect, can be used in fractured shale formations, and has good well wall stability.

[0006] The technical solution of the present invention is as follows:

[0007] An environmentally friendly well wall stabilizer, wherein the well wall stabilizer is polyvinyl alcohol-modified bupleurum saponin.

[0008] Preferably according to the present invention, the weight average molecular weight of the polyvinyl alcohol is 66,000-88,000.

[0009] The preparation method of the above-mentioned environmentally friendly well wall stabilizer comprises the steps of:

[0010] (1) dissolving polyvinyl alcohol in deionized water to obtain a polyvinyl alcohol aqueous solution;

[0011] (2) Dispersing saikosaponin in a polyvinyl alcohol aqueous solution and adjusting the pH to alkaline; reacting under stirring; adjusting the pH to neutral and drying to obtain an environmentally friendly well wall stabilizer.

[0012] Preferably according to the present invention, in step (1), the mass concentration of the polyvinyl alcohol aqueous solution is 8-12%, preferably 10%.

[0013] Preferably according to the present invention, in step (2), the saikosaponin is saikosaponin A, saikosaponin C or saikosaponin D, or a combination of two or more thereof.

[0014] Preferably according to the present invention, in step (2), the mass ratio of polyvinyl alcohol to saikosaponin is 1:0.5-0.7.

[0015] Preferably, according to the present invention, in step (2), after saikosaponin is fully dispersed in the polyvinyl alcohol aqueous solution, sodium hydroxide is used to adjust the pH to 9-11.

[0016] Preferably according to the present invention, in step (2), the reaction temperature is 60-70°C.

[0017] Preferably according to the present invention, in step (2), the reaction time is 4-6 hours.

[0018] Preferably according to the present invention, in step (2), after the reaction is completed, a hydrochloric acid aqueous solution with a mass concentration of 10-20% is used to adjust the pH to neutral.

[0019] The above-mentioned environmentally friendly wellbore stabilizer is applied to fractured shale formations to stabilize the wellbore.

[0020] The technical features and beneficial effects of the present invention are as follows:

[0021] 1. The environmentally friendly well wall stabilizer of the present invention is prepared by modifying the natural plant ingredient saikosaponin with polyvinyl alcohol. The saikosaponin structure contains many hydroxyl groups, which are grafted onto polyvinyl alcohol through etherification reaction. The preparation method of the present invention is simple and low in cost; the raw materials used and the obtained well wall stabilizer have good environmental protection.

[0022] 2. In the preparation method of the present invention, the mass ratio of saikosaponin and polyvinyl alcohol needs to be appropriate; if the amount of saikosaponin is too much, steric hindrance effect and intramolecular interaction will be formed to hinder the effect of the wellbore stabilizer on the shale; if the amount of saikosaponin is too little, an effective adsorption hydrophobic film cannot be formed, resulting in poor inhibition of shale hydration performance. The pH of the reaction of saikosaponin and polyvinyl alcohol of the present invention needs to be appropriate. If it is not in an alkaline environment, saikosaponin and polyvinyl alcohol cannot react effectively, thereby failing to achieve the excellent effect of the present invention. The polyvinyl alcohol-modified saikosaponin obtained by the reaction of saikosaponin and polyvinyl alcohol of the present invention has a specific structure as a whole, and each group has complex interactions, and only by working together can the excellent effect of the present invention be achieved.

[0023] 3. Bupleurum saponin contains a large number of hydroxyl groups in its structure. Combined with its specific structure, it can firmly adhere to the shale surface. At the same time, it has a hydrophilic and hydrophobic amphiphilic structure to change the wettability of the shale surface, thereby inhibiting the hydration of the shale; it is modified by polyvinyl alcohol to enhance its multi-point adhesion and coating performance. The Bupleurum saponin well wall stabilizer modified by polyvinyl alcohol of the present invention, as a whole, exerts the synergistic effect of polyvinyl alcohol and Bupleurum saponin, can be adsorbed on the shale surface through hydrogen bonding, etc., and forms a hydrophobic film on the shale surface to prevent the adsorption of water molecules, thereby effectively inhibiting the hydration of the shale; at the same time, the large number of hydroxyl groups on its surface and the specific structure can form a firm adhesion on different shale surfaces, thereby forming a shell layer on the shale surface to cement the shale and play a role in wall consolidation and anti-collapse to maintain the stability of the well wall.

[0024] 4. The environmentally friendly wellbore stabilizer of the present invention can effectively inhibit the hydration expansion and dispersion of shale, and at the same time has excellent chemical bonding and wall consolidation effects. It can be applied to mud shale formations, especially fractured shale formations, and has good wellbore stability. DETAILED DESCRIPTION

[0025] The present invention will be further described below by means of specific examples, but is not limited thereto.

[0026] The experimental methods described in the examples are conventional methods unless otherwise specified; the reagents and materials used are commercially available unless otherwise specified.

[0027] Example 1

[0028] A method for preparing an environmentally friendly well wall stabilizer comprises the following steps:

[0029] (1) Add deionized water to a three-necked flask equipped with a thermometer and a condenser, add a certain amount of polyvinyl alcohol (the weight average molecular weight of polyvinyl alcohol is 83600), slowly heat it to 90° C., keep it warm until the polyvinyl alcohol is completely dissolved, lower the temperature, and prepare a polyvinyl alcohol aqueous solution with a mass concentration of 10% for later use;

[0030] (2) Add the prepared polyvinyl alcohol aqueous solution to a three-necked flask equipped with a thermometer and a condenser, add saikosaponin A, the mass ratio of polyvinyl alcohol to saikosaponin is 1:0.5, fully disperse, adjust the pH to 9 with sodium hydroxide, and stir and react at 60°C for 4 hours. After the reaction is completed, adjust the pH value of the system to neutral with a 10% hydrochloric acid aqueous solution; after cooling to room temperature, dry at 55°C in a vacuum drying oven to constant weight to obtain an environmentally friendly well wall stabilizer.

[0031] Example 2

[0032] A method for preparing an environmentally friendly well wall stabilizer comprises the following steps:

[0033] (1) Add deionized water to a three-necked flask equipped with a thermometer and a condenser, add a certain amount of polyvinyl alcohol (the weight average molecular weight of polyvinyl alcohol is 74800), slowly heat it to 90° C., keep it warm until the polyvinyl alcohol is completely dissolved, lower the temperature, and prepare a polyvinyl alcohol aqueous solution with a mass concentration of 10% for later use;

[0034] (2) Add the prepared polyvinyl alcohol aqueous solution to a three-necked flask equipped with a thermometer and a condenser, add saikosaponin C, the mass ratio of polyvinyl alcohol to saikosaponin is 1:0.6, fully disperse, adjust the pH to 10 with sodium hydroxide, and stir and react at 65°C for 5 hours. After the reaction, adjust the pH value of the system to neutral with a 20% hydrochloric acid aqueous solution; after cooling to room temperature, dry at 60°C in a vacuum drying oven to constant weight to obtain an environmentally friendly well wall stabilizer.

[0035] Example 3

[0036] A method for preparing an environmentally friendly well wall stabilizer comprises the following steps:

[0037] (1) Add deionized water to a three-necked flask equipped with a thermometer and a condenser, add a certain amount of polyvinyl alcohol (the weight average molecular weight of polyvinyl alcohol is 88,000), slowly heat it to 90° C., keep it warm until the polyvinyl alcohol is completely dissolved, lower the temperature, and prepare a polyvinyl alcohol aqueous solution with a mass concentration of 10% for later use;

[0038] (2) Add the prepared polyvinyl alcohol aqueous solution to a three-necked flask equipped with a thermometer and a condenser, add saikosaponin D, the mass ratio of polyvinyl alcohol to saikosaponin is 1:0.7, fully disperse, adjust the pH to 11 with sodium hydroxide, and stir and react at 70°C for 6 hours. After the reaction, adjust the pH value of the system to neutral with a 10% hydrochloric acid aqueous solution; after cooling to room temperature, dry at 65°C in a vacuum drying oven to constant weight to obtain an environmentally friendly well wall stabilizer.

[0039] Example 4

[0040] A method for preparing an environmentally friendly well wall stabilizer comprises the following steps:

[0041] (1) Add deionized water to a three-necked flask equipped with a thermometer and a condenser, add a certain amount of polyvinyl alcohol (the weight average molecular weight of polyvinyl alcohol is 74800), slowly heat it to 90° C., keep it warm until the polyvinyl alcohol is completely dissolved, lower the temperature, and prepare a polyvinyl alcohol aqueous solution with a mass concentration of 10% for later use;

[0042] (2) Add the prepared polyvinyl alcohol aqueous solution to a three-necked flask equipped with a thermometer and a condenser, add saikosaponin A, the mass ratio of polyvinyl alcohol to saikosaponin is 1:0.6, fully disperse, adjust the pH to 9 with sodium hydroxide, and stir and react at 70°C for 4 hours. After the reaction, adjust the pH value of the system to neutral with a 20% hydrochloric acid aqueous solution; after cooling to room temperature, dry at 55°C in a vacuum drying oven to constant weight to obtain an environmentally friendly well wall stabilizer.

[0043] Example 5

[0044] A method for preparing an environmentally friendly well wall stabilizer is as described in Example 2, except that the mass ratio of polyvinyl alcohol to saikosaponin is 1:0.5; the other steps and conditions are consistent with those in Example 2.

[0045] Example 6

[0046] A method for preparing an environmentally friendly well wall stabilizer is as described in Example 2, except that the mass ratio of polyvinyl alcohol to saikosaponin is 1:0.7; the other steps and conditions are consistent with Example 2.

[0047] Example 7

[0048] A method for preparing an environmentally friendly well wall stabilizer is as described in Example 2, except that the weight average molecular weight of polyvinyl alcohol is 66,000; the other steps and conditions are consistent with Example 2.

[0049] Example 8

[0050] A method for preparing an environmentally friendly well wall stabilizer is as described in Example 2, except that the weight average molecular weight of polyvinyl alcohol is 88,000; the other steps and conditions are consistent with Example 2.

[0051] Example 9

[0052] A method for preparing an environmentally friendly well wall stabilizer is as described in Example 2, except that the mass concentration of the polyvinyl alcohol aqueous solution is 8%; the other steps and conditions are consistent with those in Example 2.

[0053] Example 10

[0054] A method for preparing an environmentally friendly well wall stabilizer is as described in Example 2, except that the mass concentration of the polyvinyl alcohol aqueous solution is 12%; the other steps and conditions are consistent with those in Example 2.

[0055] Comparative Example 1

[0056] A well wall stabilizer, as described in Example 2, except that: in step (2), the mass ratio of polyvinyl alcohol to saikosaponin is 1:2; the other steps and conditions are consistent with Example 2.

[0057] Comparative Example 2

[0058] A well wall stabilizer, as described in Example 2, except that: in step (2), the mass ratio of polyvinyl alcohol to saikosaponin is 1:0.1; the other steps and conditions are consistent with Example 2.

[0059] Comparative Example 3

[0060] A well wall stabilizer, as described in Example 2, except that: in step (2), the step of "adjusting the pH to 10 with sodium hydroxide" is omitted, that is, the pH of the reaction is about 7; the other steps and conditions are consistent with Example 2.

[0061] The specific steps of step (2) are as follows: add the prepared polyvinyl alcohol aqueous solution to a three-necked flask equipped with a thermometer and a condenser, add saikosaponin C, the mass ratio of polyvinyl alcohol to saikosaponin is 1:0.6, fully disperse and react at 65°C with stirring for 5 hours. After the reaction is completed, cool to room temperature and dry in a vacuum drying oven at 60°C to constant weight to obtain an environmentally friendly well wall stabilizer.

[0062] Comparative Example 4

[0063] A well wall stabilizer, wherein the well wall stabilizer is polyvinyl alcohol with a weight average molecular weight of 74800.

[0064] Comparative Example 5

[0065] A well wall stabilizer, wherein the well wall stabilizer is saikosaponin.

[0066] Comparative Example 6

[0067] A well wall stabilizer, as described in Example 2, except that: in step (2), the reaction temperature is 30°C; the other steps and conditions are consistent with Example 2.

[0068] Comparative Example 7

[0069] A well wall stabilizer, as described in Example 2, except that: in step (2), the reaction temperature is 90°C; the other steps and conditions are consistent with Example 2.

[0070] Comparative Example 8

[0071] A well wall stabilizer, as described in Example 2, except that in step (2), saikosaponin is replaced by catechol; the other steps and conditions are consistent with Example 2.

[0072] Test Example 1

[0073] 10g of dried sodium bentonite was placed in a die and pressed with a hydraulic press at 10MPa for 10 minutes to obtain a bentonite core sample. A portion of 1wt% aqueous solution of the example and comparative sample was prepared, and the core samples prepared above were added respectively (the core samples were immersed in the solution), and the expansion height of the core samples immersed at room temperature for 24 hours was measured using a shale dilatometer. At the same time, a control group without a well wall stabilizer sample was set up, that is, the core samples prepared above were added to distilled water, and the expansion height of the core samples after being immersed at room temperature for 24 hours was measured using a shale dilatometer; the linear expansion rate was calculated, that is: (height after expansion-height before expansion) / height before expansion.

[0074] Table 1 Linear expansion rate

[0075]

[0076]

[0077] It can be seen from Table 1 that, compared with distilled water, in the 1% well wall stabilizer solution prepared in the embodiment of the present invention, the linear expansion rate of bentonite is lower, showing excellent inhibition performance.

[0078] Test Example 2

[0079] The wellbore stabilizer prepared in the embodiment or comparative example is formulated into a wellbore stabilizer aqueous solution with a mass concentration of 1%, 50g of dried (dried at 103°C for 10h) shale cuttings that have passed through a 6-10 mesh sieve is added, and then the mixture is transferred to an aging tank and hot-rolled at 120°C for 16 hours. When it cools to room temperature, it is poured into a 40-mesh standard sieve, rinsed with tap water for 1 minute, and the remaining cuttings on the standard sieve are dried at 103°C for 4 hours and weighed. The rolling recovery rate of shale cuttings is the ratio of the weight of the cuttings remaining after hot rolling to the weight of the cuttings used before hot rolling. At the same time, a control group without wellbore stabilizer is set up, that is, the above test is carried out in distilled water.

[0080] Table 2 Rolling recovery rate

[0081]

[0082]

[0083] It can be seen from Table 1 and Table 2 that the wellbore stabilizer of the present invention exhibits excellent inhibitory performance. The poor performance of Comparative Example 1 is due to the excessive amount of saikosaponin, which forms a steric hindrance effect and intramolecular interaction that hinders the effect of the wellbore stabilizer on shale; Comparative Example 2 is due to the fact that the amount of saikosaponin is too small to form an effective adsorption hydrophobic film, resulting in poor inhibition of shale hydration performance; in Comparative Example 3, since the pH is 7, it is not in an alkaline environment, saikosaponin and polyvinyl alcohol cannot react effectively; Comparative Examples 4 and 5 only have one of polyvinyl alcohol and saikosaponin, and cannot effectively form a hydrophobic film, and the inhibitory effect is not strong enough.

[0084] Test Example 3

[0085] The well wall stabilizer prepared in the embodiment or comparative example was prepared into a well wall stabilizer aqueous solution with a mass concentration of 1%, and a 50×25 mm standard core was immersed in the solution at room temperature for 24 hours, then taken out and dried, and the compressive strength of the shale core was tested under a universal testing machine. At the same time, a control group without well wall stabilizer was set up, that is, the above test was carried out in distilled water.

[0086] Table 3 Compressive strength of shale samples before and after modification

[0087]

[0088]

[0089] It can be seen from Table 3 that the original core compressive strength is 112 MPa, and the strength of the shale treated with distilled water decreases to 68 MPa. However, after being treated with the wellbore stabilizer of the present invention, the strength of the shale is greatly improved to 115 MPa, which shows that the wellbore stabilizer of the present invention has an efficient wall-fixing effect on shale and can significantly improve the wellbore stability.

[0090] Test Example 4

[0091] The biological toxicity and biodegradability of the wellbore stabilizer in Example 2 were tested.

[0092] Determine EC according to GB / T15541-1995 standard 50 value.

[0093] The BOD and COD values ​​of the aqueous solution of the well wall stabilizer prepared in Example 2 with a mass concentration of 1% were tested according to GB / T 11914-2017 and HJ 505-2009 standards, and the BOD / COD was calculated (if BOD / COD ≥ 25, the biodegradability classification is easily degradable). The results are shown in the following table.

[0094] Table 4 Biological toxicity and biodegradability

[0095] sample <![CDATA[EC 50 / mg·L -1 ]]> BOD / COD(%) Example 2 97000 38.2

[0096] Table 4 shows the biotoxicity and biodegradability of the well wall stabilizer prepared in Example 2, indicating that it is non-toxic, easily biodegradable, and green and environmentally friendly.

[0097] In summary, the wellbore stabilizer of the present invention can effectively inhibit the hydration of shale, cement the formation, maintain the stability of the wellbore, and meet the needs of drilling in fractured shale formations.

[0098] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0099] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0100] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. An environmentally friendly well wall stabilizer, characterized in that: The well wall stabilizer is polyvinyl alcohol-modified saikosaponin; The preparation method of the environmentally friendly well wall stabilizer comprises the following steps: (1) dissolving polyvinyl alcohol in deionized water to obtain a polyvinyl alcohol aqueous solution; (2) fully dispersing saikosaponin in a polyvinyl alcohol aqueous solution and adjusting the pH to alkaline; reacting under stirring conditions; adjusting the pH to neutral and drying to obtain an environmentally friendly well wall stabilizer; In step (2), the mass ratio of polyvinyl alcohol to saikosaponin is 1:0.5-0.7; after saikosaponin is fully dispersed in the polyvinyl alcohol aqueous solution, sodium hydroxide is used to adjust the pH to 9-11; the reaction temperature is 60-70°C.

2. The environmentally friendly well wall stabilizer according to claim 1, characterized in that: The weight average molecular weight of polyvinyl alcohol is 66,000-88,000.

3. The environmentally friendly well wall stabilizer according to claim 1, characterized in that: In step (1), the mass concentration of the polyvinyl alcohol aqueous solution is 8-12%.

4. The environmentally friendly well wall stabilizer according to claim 1, characterized in that: In step (2), the saikosaponin is one of saikosaponin A, saikosaponin C or saikosaponin D, or a combination of two or more thereof.

5. The environmentally friendly well wall stabilizer according to claim 1, characterized in that: In step (2), the reaction time is 4-6 hours.

6. An application of the environmentally friendly well wall stabilizer according to any one of claims 1 to 5, characterized in that: Applied to fractured shale formations to stabilize the wellbore wall.

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